Bilingual adults often engage in language-mixing behavior (i.e., mixing two languages in the same discourse) yet hold varied attitudes toward it (Poplack, 1988). Past research suggests that bilingual parents’ language attitudes (e.g., one should cherish mother tongue) do not necessarily predict their language choices in interactions with their children (Ghimenton, 2015; Yu, 2010). In the current study, we examine the relationship between parental attitudes toward language-mixing and their self-reported use of language-mixing in conversation with their own child, and the moderation effect of the child’s mother tongue (MT) language use. This is part of a larger project on children’s language and socio-cognitive development. Parents (N=231) of 2-6 year old English-Chinese bilingual children completed a questionnaire, in which they reported (1) how often they engage in language-mixing behavior (e.g., “I switch languages within a sentence”) when talking to their child, (2) their attitudes toward language-mixing (e.g., “People should speak only one language at a time), and (3) percentage of time their child hears and speaks MT (Chinese). Regression analyses revealed that parental language-mixing behavior was significantly predicted by their attitudes toward language-mixing (b=-.45, p<.001). Overall, parents who expressed more negative attitudes toward language-mixing reported less use of language-mixing than those with more positive attitudes. However, this relationship was moderated by the child’s MT usage (p<.01): For children with lower MT usage, the frequency of parental language-mixing was low and did not vary with parental attitudes, whereas for children with higher MT usage, parents with less negative attitudes toward language-mixing reported more language-mixing behavior than parents with more negative attitudes. The study provides important insights into how bilingual parents’ attitudes and their child’s language usage influence their language-mixing practices.