We studied group types and sizes of blue sheep (Pseudois nayaur) in the Helan Mountains from November 2004 to October 2005. Blue sheep groups were observed with KOWA 8×42 DCF binoculars and a KOWA TSN-824 M power spotting scope. Groups were classified as female, male, male-female, ewe-lamb, mixed groups, and solitary sheep. A total of 4 866 sheep belonging to 1 023 groups were observed, with a mean group size of 4.86 (SD=2.54). The largest groups included 51 sheep and the smallest groups were solitary sheep. Ewe-lamb groups were the most frequently encountered, constituting 44.8% of total observations. Mixed-sex groups, male groups and solitary sheep made up 20.72%, 14.68%, and 9.09% respectively of total observations. Male-female and female groups made up 5.57% and 4.89% of total sheep classified. Ewe-lamb groups predominated in all seasons, but frequencies of observed group types varied seasonally (P<0001). Male groups were more numerous in spring than in other seasons, whereas mixed groups were least in spring, increasing through summer, autumn, and winter. Groups consisting of 2-5 individuals dominated in all seasons, and constituted 50% of total groups observed. Group sizes varied seasonally (P<0.001), but mean group size did not differ seasonally. There were significant seasonal variations in group sizes of mixed-sex (P<0.001), ewe-lamb (P<0.05), and female groups (P<0.05). Seasonal variations in sizes of male and male-female groups were not significant. Small herd sizes are characteristic of the blue sheep in the Helan Mountains.