Sex differences in social and communication behaviours related to autism spectrum conditions (ASC) have been investigated mainly in Western populations. Little research has been done in Chinese populations. This study explored sex differences related to ASC characteristics by examining differences in item responses and score distributions in relation to a screening instrument, the Childhood Autism Spectrum Test (CAST), used with Chinese children. A Mandarin Chinese version of the CAST (M-CAST) was distributed to 737 children aged 6-11 years in mainstream schools in Beijing. Questionnaires from 682 (93 %) children were available for analysis. The median score for boys was higher than for girls [boys, median = 8 (IQR 6, 11); girls, median = 7 (IQR 4, 9); p < 0.001]. There were differences in the proportions of boys and girls across all three score groups (=11, 12-14, =15) with more boys being found in the higher score groups (p = 0.035). This finding provides evidence that boys and girls have different social and communication development profiles, consistent with previous findings in Western cultures. These results suggest that sex differences related to ASC are consistent across cultures.