SUMMARY One hundred and one Ossimi ewes were used to study the effect of order of mating after PGF2α estrus synchronization on conception rate (CR). Ewes were weighed and scored for body condition and rams were tested for their semen by semen analysis immediately before onset of mating. Ewes were estrus-synchronized with intramascular dose of 0.5 ml PGF2α, and after 11 days of the first injection ewes that did not show estrus were injected with another 0.5 ml dose. Simultaneously, with the first and the second injections of Estrumate, ewes which came in heat were introduced to fertile rams to be hand-mated. ANOVA were performed to study the effect of CR of ewes at the first and the second estrus matings, and also to study the effect of age, body weights (BWT) and body condition scores (BCS) of ewes on CR at the first and the second estrus matings. Correlation coefficients between CR of ewes and their ages, BWT and BCS were performed. About 77% of mated Ossimi ewes in the second estrus mating were fertilized compared to only 18% in the first one (P<0.001). At the first estrus mating, the significance level (P<0.05) was attained for the correlation of CR with BCS of ewes, while it was not attained for both age of ewes or their body weights. Body condition scores of ewes significantly affected CR at first estrus mating (P=0.017). Therefore, it is recommended to breed ewes at the second heat after estrus synchronization with PGF2α to save the power of rams and preserve their capabilities for increasing CR through the second estrus after synchronization.