Abstract: Objective To evaluate the relationship between birth weight and nonalcoholic fatty liver diseases (NAFLD) in Chinese primary school students. Methods A cross-section study was conducted in five elementary schools in Gao Hang Town, Shanghai and 2163 students were enrolled in the study (1120 boys/1043 girls). Height, body weight, waist circumference and percent of body fat (bioelectrical impedance analysis) were measured by professional nutritionist after training. Birth weight, feeding pattern, height and body weight of parents were obtained by a self-completed questionnaire. NAFLD was diagnosed by ultrasound. The risk factors of NAFLD were analyzed. Results The prevalence of NAFLD in the study population was 8.9%. The prevalence of NAFLD was significantly higher in boys than that in girls (12.5% vs 5.0%, P<0.01). Logistic regression showed that sex (OR=1.97, 95%CI: 1.21-3.21) and percent of body fat (OR=1.12, 95%CI: 1.07-1.17) were the risk factors of NAFLD, and normal BMI was the protective factor of NAFLD (OR=0.09, 95%CI: 0.04-0.19) in the study population. Conclusions The prevalence of NAFLD is higher in boys than that in girls. Also overweight, and high percent of body fat are risk factors of NAFLD in children.