Abstract: Objective To study the effects of overweight and obesity on children's learning achievement and mental health.Methods A total of 1 582 grade 3 students from 5 elementary schools in Taiyuan city were selected with random cluster sampling method.Primary and secondary mental health scales were performed for the studetns to evaluate their mental health status.Results The prevalence rate of overw eight and obesity in the students were 11.5% and 9.4%.The prevalence rates of overw eight and obesity were significantly higher in the boys(14.4% and 12.2%)than in the girls(8.5% and 6.5%).The learning achievement of normal children(188.95±10.76)was significantly better than that of obesity children(186.56±9.83)and the total score of mental health of normal children(466.83±52.07)was significantly better than that of obesity children(453.25±56.41).Multiple stepw ise regression analyses show ed that learning scores,father's educational level and mother's educational level were the main influence factors of children's learning achievement,and mother's educational level,gender and children's body mass index were the main influence factors of children's mental health.Conclusion The effect of obesity on children's learning achievement and mental health is significant.