Background and aims: Existing studies that simultaneously consider the effects of lifestyle and family environment factors on mental health problems (MHPs), particularly in preschoolers, are limited. This study aims to explore lifestyle and family environment factors associated with MHPs, externalising problems (EPs) and internalising problems (IPs) in preschoolers. Methods: This territory-wide, school-based study conducted from 2020 to 2022 involved 1926 preschoolers. MHPs, EPs, and IPs and factors such as sleep duration, sleep latency, entertainment screen time, educational screen time, parent-child recreation and learning activities were assessed. Linear and logistic regression analyses were used to explore the relationships between these factors and MHPs, EPs, and IPs. Results: The average sleep duration was 9.94 h per day, average screen time of 2.53 h per day, and 42.6 % experienced sleep latency exceeding 20 min per day among preschoolers (mean age: 4.39 years, 49.1 % female). Adjusted analyses showed that decreased parent-child recreation activities, prolonged sleep latency and excessive entertainment screen time were associated with increased MHPs, EPs, and IPs (β: 0.05 to 0.20, all p < 0.05). Weekend sleep duration of <10 h per day, sleep latency of >20 min per day, and educational screen time of >30 min per day were identified as risk factors for MHPs, EPs, and IPs, with an adjusted odds ratio ranging from 1.32 to 2.32 (all p < 0.05). Conclusions: Preschoolers' lifestyle and family environment factors are associated with MHPs, EPs, and IPs respectively. Ensuring adequate sleep duration, avoiding sleep latency exceeding 20 min per day, reducing entertainment screen time, limiting educational screen time to 30 min per day, and increasing parent-child interactions may help to minimise mental health problems. Copyright © 2025 The Authors.