Group pattern and social segregation of the sexually size dimorphic Przewalski's gazelle Procapra przewalskii were studied for 7 years in the Qinghai Province, China. The main social units were: female groups; male groups; mixed groups. Mixed groups were the largest and most visible, whereas adult male groups were small and of similar size. The group size of the gazelle varied during different seasons (P < 0.002) and the type of social groups (P < 0.001). Mixed-sex groups were larger than female groups or male groups across all the seasons (P < 0.008). Adult males and females were mainly in separate groups except during the rut. Groups of adult females were the most common social unit in Przewalski's gazelle, followed in frequency by adult male groups and mixed groups. From late June to late August, social separation was most pronounced. From late October to mid-September, social segregation was not pronounced. Social segregation showed significant seasonal differences in Przewalski's gazelle (P < 0.004), especially between the rut and other seasons (P < 0.008). The pattern of social segregation of groups and behaviours observed imply that social factors play important roles in social segregation and group formation.