This study investigated the variation of subject pronominal expression in Mandarin Chinese. The data were collected from 20 speakers in three discourse contexts including informal conversations, elicited narratives, and teacher classroom speech. A multivariate analysis of 8,507 tokens revealed that the linguistic constraints that affect Chinese subject pronoun use include switch in subject referents, person/number/animacy of the subject, specificity of subject referents, and sentence type. In regards to social factors, age, gender and occupation were significant. Older speakers/teachers/females are more likely to realize subject pronouns than younger speakers/students/males.