The purpose of this study was to evaluate the relationships between screen time (ST), nighttime sleep duration, and behavioural problems in a sample of preschool children in China. A sample of 8900 children aged 3-6 years was enrolled from 35 kindergartens, in four cities, in two provinces, in China to evaluate the relationships between ST, nighttime sleep duration, and behavioural problems. Children’s ST and nighttime sleep duration were assessed by questionnaires completed by parents or guardians. Behavioural problems were assessed using the Strengths and Difficulties Questionnaire (SDQ), and the Clancy Autism Behaviour Scale (CABS). Multivariate analysis was used to assess the associations between ST, nighttime sleep duration, and behavioural problems. The total SDQ and CABS scores were higher in children with ST >/=2 h/day and sleep duration <9.15 h/day (a P < 0.001 for all). After adjusting for potential confounders, children with ST >/=2 h/day had a significantly increased risk of having total difficulties, emotional symptoms, conduct problems, hyperactivity, peer problems, and prosocial problems, as well as behavioural symptoms of autism spectrum disorder. Similar results were found in children with sleep duration <9.15 h/day. No significantly increased risk of emotional symptoms was observed for short sleep duration. Preschool children with more ST and short nighttime sleep duration were significantly more likely to have behavioural problems. These results may contribute to a better understanding of prevention and intervention for psychosocial problems in children.