Research increasingly indicates that expressive flexibility is a marker for adaptive functioning, yet the role of family environment in shaping youth’s expressive flexibility remains uninvestigated. The present study examined between- and within-family associations between family expressiveness and early adolescents’ expressive flexibility via Random Intercept Cross-Lagged Panel Modeling (RI-CLPM). A total of 274 Chinese adolescents (Mage = 13.56) reported perceptions of family expressiveness and expressive flexibility at six-month intervals over one year. At the between-family level, expressive flexibility was positively correlated with positive family expressiveness and negatively correlated with negative family expressiveness. At the within-family level, increased positive family expressiveness predicted later improvement in adolescents’ expressive flexibility, but changes in negative family expressiveness did not predict subsequent expressive flexibility. Results support the importance of family emotional climate for adolescents’ adaptive emotion regulation. Promoting a climate that adolescents perceive as positively expressive might be particularly beneficial for their development of expressive flexibility.