A growing body of literature shows that adherence to some aspects of Western masculinity norms, including the suppression of emotional vulnerability, avoidance of seeking support from others, and exaggerated physical toughness, is associated with poorer psychological and social outcomes. While existing research suggests that parental gender beliefs and caregiving behaviors might influence the development of children's gendered behaviors, little is known about the developmental origins of individual differences in adherence to masculinity norms. The current study aims to address this gap and presents a longitudinal investigation of how parental gender beliefs and maternal sensitivity during infancy contribute to children's adherence to masculinity norms during middle childhood. Data were drawn from a mixed-method 9-year longitudinal study of 374 urban Chinese families (48.40% with daughters). Parental gender beliefs were assessed at 24 months, maternal sensitivity was assessed with mother-child interaction observations at 14 and 24 months, and children's self-reported adherence to masculinity norms were assessed at age 10 years. Results indicate that while parental gender beliefs had no associations with children's adherence to masculinity norms, maternal sensitivity predicted children's adherence to masculinity norms ([beta] = -0.18, p = 0.008) above and beyond parental gender beliefs and parental education level; moreover, there was a significant interaction of sex on the effect of maternal sensitivity on children's adherence to masculinity ([beta] = -0.23, p = 0.025), and the association was significant only for boys.