Background: Male fertility requires proper functioning testes and proper hormonal balance as well. Thyroid hormones (T3 and T4) have been described to be a risk factor in male infertility. L-carnitine (LC) is an amino acid derivative that regulates long chain fatty acids metabolism and possess an antioxidant activity. Aim of Work: It was to evaluate the effect of induced hyperthyroidism on adult albino rats’ testes and the possible ameliorating role of LC. Material and Method: Twenty-four adult male albino rats have been used in this work. They were randomly divided into three groups with eight animals in each group. Group I (Control). Group II (l-thyroxine (T4)-treated): Animals were subjected to administration of 2 μg/ml/day l-thyroxine orally. Group III (T4 and LC-treated): Animals were subjected to administration of the same dose of l-thyroxine and LC at a dose of 500 mg/kg via intraperitoneal injection. By the end of the experiment that was 30 days; hormonal essay, semen analyses were done. Specimen of testes was prepared for light microscopic examination using hematoxylin and eosin stain, Mallory’s trichrome stain and immunohistochemical stain with PCNA. In addition, morphometrical studies were performed and statistical analysis of results. Results: Induced hyperthyroidism caused loss of germinal epithelium with gaps among spermatogenic cells which was confirmed by decrease in height of seminiferous tubules. There was loss of active spermatogonia which was confirmed by significant decrease in PCNA immunostaining. Some tubular lumina showed absence of sperms and spermatids and others showed exfoliated nuclei and multinucleated giant cells. LC protected the testicular specimens against such changes; it improved seminal quality and quantity as well as testicular structure and biochemistry. Conclusion: Hyperthyroidism could harm the structure of testis. Fortunately, administration of LC to these cases is suggested to reduce the associated hazards.