Abstract: In this research slaughtered sheep and goats were investigated during August 2003-July 2004 at a slaughterhouse in Masjed-Soleyman, South-Western Iran. The number of infested animals with Przhevalskiana larvae and their age and sex was recorded. Collected larvae from infested animals were stored in Alcohol-Glycerin solution and were studied to determine their morphological properties and species. The data was analyzed by the chi-square test. Rate of infestation was 0.2 and 5.3% in sheep and goats, respectively. Infestation rate in male and female goats and sheep was significantly different (p<0.05). Prevalence of hypodermosis in sheep was significantly different in spring and winter, while infestation prevalence in goats was significantly different in four seasons of the year. Myiasis was seen more frequent in 2-3 and 1-2-year-old age groups of sheep and goats, respectively. The causative agents of goat and sheep hypodermosis were Przhevalskiana aegagri and Przhevalskiana crossii. The onset of fly activity was from late June to mid July.