Stomach horse bots, the larvae of the Gasterophilus intestinalis flies (bot flies), inhabit the stomach of equines and cause damage ranging from mild gastritis to stomach ulcers and peritonitis. The adult flies are non-parasitic and incapable of feeding, yet they survive on the nutrients left from the larval stage for approximately 10-14 days, a period long enough for them to mate and lay eggs. In this study, morphological characterization of adult fly, second and third larval stages of G. Intestinalis (Diptera: Oestridae) is illustrated using light and scanning electron microscopes (SEM). The later clarifies the structures of cephalic segment, sensory array of distal maxilla (mouth hooks), thoracic and abdominal spines and terminal abdominal segment of second instar and third instar. Morphological differences between second and third stage larvae of G. intestinalis are also discussed in this work. Adult fly antennae and antennal sensilla are studied using SEM, each antenna consisted of scape, flattened disc like pedicel, pyriform funiculus and arista. Funiculus had five types of sensilla (trichoid, basiconic, coeloconic, clavate and auriculate). Arista was composed of one or two short basal segments without sensilla and one long distal segment covered with coeloconic III sensilla. It is concluded that light and SEM should be used in conjunction for the description of G. intestinalis but SEM is considered superior in description of their ultrastructure. Finally, pathological lesions in the stomach wall of infested donkeys are described.