Abstract: This study aimed to characterize the reproductive regulation of Dorper sheep and Mongolian sheep crossbred ewes. The recorded data of first estrus, gestation period, lambing rate, twinning rate and other reproductive indicators of the crossbred ewes （n=668） raised in Siziwang Banner of Ulanqab City of Inner Mongolia were collected and collated; the estrous cycle and duration of estrus of the crossbred ewes （n=302） was observed by ram mating test. The data of the above reproductive indicators of the two ewe herds were analyzed to reveal the reproductive regulation of the crossbred ewes raised in this region. The results showed that the presence of the first estrus of the crossbred ewes was averagely observed at the age of 8.5 months （the earliest at the age of 7.0 months, the latest at the age of 10.7 months); the average estrous cycle of the crossbred ewes was 16.0 d （the shortest was 13.5 d, the longest was 18.5 d）; the duration of estrus of the crossbred ewes averagely lasted for 24.0 h （the shortest lasted for 20.0 h, the longest lasted for 27.5 h）; the average gestation period of the crossbred ewes was 146.0 d （the shortest was 143.0 d, the longest was 149.0 d）; the lambing rate and twinning rate of the crossbred ewes was 119.7% and 19.7%, respectively. The results obtained in this study provide a basis for understanding the natural estrus regulation of Dorper sheep and Mongolian sheep crossbred ewes and accurately grasping the best breeding time.

Key words: Dorper sheep and Mongolian sheep crossbred ewes, natural estrus, reproductive regulation