BACKGROUND: Although previous studies have shown that children from disharmonious families were more likely to exhibit behavioral problems, the underlying pathways remain unclear. This study aimed to assess the associations between family disharmony and behavioral problems among Chinese preschool children and to investigate the potential mediating role of maternal negative emotional states. METHODS: A cross-sectional study including 4243 preschool children and their mothers was conducted in Chengdu, China. Mothers reported the level of family disharmony and their negative emotional states, including depression, anxiety, and stress. They also reported their children's behavioral problems using the Conners' Parent Rating Scale-48 items. Generalized structural equation models and bootstrapping methods were used to explore the mediating role of maternal negative emotional states in the associations between family disharmony and children's behavioral problems. RESULTS: Preschool children from disharmonious families had a significantly higher prevalence of behavioral problems. Family disharmony was positively associated with various behavioral problems across multiple domains. In addition, maternal negative emotional states partially mediated these associations, with mediation proportions ranging from 49.63 % for anxiety to 63.96 % for impulsive-hyperactive. LIMITATIONS: The cross-sectional design limited causal inferences. CONCLUSION: Our study highlighted the significant impact of family disharmony on preschool children's behavioral problems and confirmed the mediating role of maternal negative emotional states. The findings suggested that implementing interventions aimed at improving family harmony and addressing maternal negative emotions may effectively reduce the risk of behavioral problems among Chinese preschool children. Nevertheless, future randomized controlled trials are needed to confirm the conclusions.