Objective To study the effect of physical activities and dietary intervention on metabolic syndrome (MS) in primary school students.Methods Either one-year physical activities (PA) or dietary intervention was conducted in Grade 1-5 children from eight primary schools in Haidian district,Beijing.A ‘happy 10 minutes' program was held in the PA group,while the dietary group receiving nutrition lectures.Baseline and post-intervention data on height,weight,waist circumference,serum lipids,glucose,and blood pressure were collected.Results The prevalence of MS at baseline was 9.0％.After intervention programs were carried out,improvements on triglyceride,high density lipoprotein,fasting blood glucose,diastolic blood pressure and waist circumference in the dietary group or PA group were seen,with the dietary group showed better effects than the PA group.The prevalence of MS decreased from 10.4％ to 4.6％ in the dietary group with statistically significant difference,while it increased in both the PA group and the control group.Girls showed better effects in the dietary group.Older students showed better effects than the younger students in the PA group.In non-overweight and overweight students of the dietary intervention group,the MS related components were significantly improved.Conclusion The prevalence of metabolic syndrome was relatively high in the primary school students in Beijing.Education on nutrition could reduce the prevalence and improve the related components,which seemed to be more effective than in the PA intervention.Sex,age and nutritional status were the confounding factors for intervention programs.