This study aimed to verify the sex differences in early syntactic development among Cantonese-speaking children by Tse et al. (2002), with the same corpus design but a different Chinese language: Mandarin. The utterances produced during half-hour play activities by 192 Beijing children, ranging from 3 to 6 years, were collected in the Early Child Mandarin Corpus (Li & Tse, 2011) and analyzed for this study. Their syntactic development was measured in terms of mean length of utterance (MLU), sentence type and structure, syntactic complexity, and verb pattern. The statistical analyses indicated significant age differences in MLU, sentence types and structures, and syntactic complexity. However, no sex or age-by-sex differences were found. This negative evidence indicates that sex difference is neither universal nor cross-language. The implications for early childhood education and future studies are discussed.