Objective To explore the accuracy of college students' social cognition of their acquaintances' personalities, and the differences in accuracy between male and female students. Methods 84 participants were tested with Big Five Inventory to evaluate their acquaintances' personalities, while their acquaintances were tested to evaluate their own personalities.Results In the female group, a correlation between the participants' perceptions of their acquaintances and the acquaintances' self-perception turned out to be significant in dimension of extroversion(r=0.564,P<0.01) and in openness(r=0.508,P<0.01);however, in dimensions of neuroticism,extroversion and conscientiousness,significant differences were found (21.20±3.95 vs 24.76±5.01,t=4.254,P<0.01;27.33±5.36 vs 25.42±5.53,t=2.519,P<0.05; 30.76±5.18 vs 28.51±4.85, t=2.384,P<0.05);In the male group, correlation only existed in extroversion (r=0.404,P<0.05); in dimensions of extroversion and conscientiousness, differences were significant (28.28±5.21 vs 25.90±5.10,t=2.646,P<0.05;30.75±5.37 vs 28.18±5.81,t=2.315,P<0.05). Conclusions The accuracy of college students' social cognition of their acquaintances' personalities varies both in personality dimensions and in gender; students tend to evaluate their acquaintances' personalities as those which will conform to social expectancy or be of a benefit to their acquaintances.