This study was conducted on thyroid gland samples collected during different seasons of the year (twenty per season) and twenty parathyroid gland samples of adult male goats. Both glands were removed from apparently healthy animals immediately after slaughter. The specimens for light microscope were fixed in 10% neutral buffered formalin and processed by paraffin technique. Sections of 5μm thickness were obtained. The underwent H&E, Silver impregnation technique, Crossmon's trichrome stain, Orcein stain, AB (pH 2.5), PAS technique, and Periodic Acid Schiff (PAS)-Alcian blue pH (2.5) combination. Anatomical structure: The goat's thyroid gland is a bilobed organ; consisted right and left lobes without an isthmus, and located along the lateral aspect of the trachea. Right lobe has rounded cranial end and pointed caudal end. Left lobe, elongated in shape, has a less pointed cranial end and pointed caudal end. Ultimobranchial body remnants appear as a white mass at the end of the cranial one-third of the thyroid lobe, found deeply inside thyroid tissue at a distance 0.5 cm from the cranial end and 0.5 cm from the medial border of thyroid lobe. Parathyroid glands consist of two pairs; external pair (Right and Left) and internal pair (Right and Left). External parathyroid glands might be surrounded by the remnants of thymic tissue, and are located anterior to the cranial pole of the right and left lobe of thyroid gland. Internal parathyroid gland embedded inside thyroid tissue could be seen after making serial sections in the formalinized thyroid lobes. Light Microscopy: Thyroid gland is surrounded by a connective tissue capsule, which has arising septa dividing the thyroid's parenchyma into several lobules; each lobule formed from numerous number of thyroid follicles with different sizes and shapes. In summer, most of the follicles were lined with low cuboidal or simple squamous epithelium, have homogenous and evenly distributed colloid; while, these follicles were lined with high cuboidal epithelium with highly vacuolated colloid in winter. In spring, similar results to those of summer were detected but the lining epithelium was higher in height with paler nuclei. However in autumn, the histological findings were not identical to those of winter where most of these follicles had highly vacuolated colloid. It had larger thyroid follicles than in the winter season. Parafollicular cells were seen between the follicular cells, basally located and not reach the luminal colloid. Parafollicular cells are larger in size than the follicular epithelium. They are rarely found in thyroid sections. They are polyhedral or pyramidal in shape with oval or rounded nuclei and lightly stained acidophilic cytoplasm. Most of these follicles are surrounded by a thin sheet of spindle -shaped myoepithelial cells with flattened nuclei. They are found between the basal part of the follicular epithelium and basement membrane. External parathyroid gland is surrounded by remnants of thymic tissue. It is surrounded by a connective tissue capsule, which gives short and thick septa dividing the parenchyma into incomplete lobules. The latter had densely packed cellular structures separated by numerous blood capillaries. The gland parenchyma consisted of only chief cells, which are classified into two types; darkly stained cells and lightly stained cells with round shape and pale acidophilic highly vacuolated cytoplasm. Internal parathyroid gland is embedded inside thyroid tissue where it is surrounded by the thyroid follicles. The internal parathyroid gland is similar in structure to the external parathyroid gland. Immunohistochemical studies: Thyroid follicular cells and the luminal colloid are strongly reacted to thyroglobulin antibodies. Ultimobranchial body remnants are positively reacted to P63 antibody. The reaction includes small thyroid follicles and peripheral cells of the solid cell nests while its central cells are negatively reacted to the P63 antibody. During the summer season, myoepithelial cells surrounding the thyroid follicles are negatively reacted to the desmin antibody, while they are positively reacted to desmin antibody during the other seasons. They appeared as a girdle like structure surrounding the follicles. Parafollicular cells are found between the follicular epithelium and not reach the lumen, are positively reacted to calcitonin antibody. Also, they are reacted against S-100 protein and appeared as darkly stained cells. Immunohistochemical observation of parathyroid gland revealed that chromogranin immunoreactive cells showed a strong positive reaction with anti-chromogranin, especially in the cytoplasm of chief cells around the nuclei. The chief cells appeared in form of aggregates which are homogenously and equally stained. Scanning electron microscopic studies: Thyroid gland consists of numerous thyroid follicles, which varied in size and shape. In the summer season, they appeared in form of small, medium, and large follicles, and their shapes vary from oval to polygonal or irregular in shape. While in the winter season, these follicles are engorged with colloid droplets. In the autumn season, some of these follicles are filled with colloid and some are empty. Transmission electron microscopic studies: In the summer season, the thyrocytes have a moderate number of cell organelles includes some colloid droplets, lysosomes, and mitochondria. The follicular cells had irregular nuclei with some rough endoplasmic reticulum. However, the follicular cells had euchromatic nuclei, elongated mitochondria, rounded lysosomes, several colloid droplets. They also had some rough endoplasmic reticulum in the autumn season. In the winter season, the ultrastructural features of thyroid follicles showed that follicular cells are highly columnar in shape, engorged with colloidal secretion with ovoid compressed nuclei, electron-dense colloid droplets, mitochondria, and lysosomes. Parafollicular cells present below the follicular cells and not reach the follicular lumen with centrally located nuclei, elongated mitochondria, and several granules with electron-dense contents. Parafollicular cells are found mainly near blood capillary. The neighboring follicles are isolated by interfollicular connective tissue containing collagen fibers, fibroblast cells, and interfollicular cells. These interfollicular cells have heterochromatic nuclei without secretory granules. Thyroid follicles are surrounded by a thin sheet of spindle-shaped myoepithelial cells with intense cytoplasm where it contains some myofilaments and characterized by long cytoplasmic processes. Ultimobranchial body remnants like cells showed some cells between thyroid follicles. These cells had rounded, central heterochromatic nuclei with clear cytoplasm without any granules. Also, ultimobranchial body remnants also had a numerous number of parafollicular cells which present below follicular cells. These parafollicular cells had darkly stained granules and paler granules. External parathyroid gland, ultrastructural features showed some chief cells, which are classified into active and inactive chief cells. The active chief cells are polygonal in shape with several supranuclear Golgi apparatus, rough endoplasmic reticulum, mitochondria, and secretory granules. The inactive chief cells had a polygonal shape, their cytoplasm had mitochondria, several autophagic vacuoles, little secretory granules, and some storage granules. Internal parathyroid gland demonstrated that it consisted of chief cells with ovoid nuclei with some mitochondria, several rough endoplasmic reticulums, numerous secretory granules, and storage granules.