Objective This study aimed to evaluate the associations of serum folate and/or vitamin B12 concentrations with obesity among Chinese children and adolescents. Methods A cross-sectional study was conducted including 3,079 Chinese children and adolescents,aged 6 to 17 years,from Jiangsu,China.Anthropometric indices,such as,children's body mass index(BMI),BMI z-scores,waist circumference,and waist-to-height ratio were utilized.Multivariable linear regression and generalized additive models were used to investigate the associations of serum folate and vitamin B12 levels with anthropometric indices and odds of obesity. Results We observed that serum vitamin B12 concentrations were inversely associated with all anthropometric indices and the odds of general obesity[odds ratio(OR)= 0.68;95%confidence interval(CI)= 0.59,0.78]and abdominal obesity(OR = 0.68;95%CI = 0.60,0.77).When compared to participants with both serum vitamin levels in the two middle quartiles,those with both serum folate and vitamin B12 levels in the highest quartile were less prone to general(OR = 0.31,95%CI = 0.19,0.50)or abdominal obesity(OR = 0.46,95%CI = 0.31,0.67).Conversely,participants with vitamin B12 levels in the lowest quartile alongside folate levels in the highest quartile had higher odds of abdominal obesity(OR = 2.06,95%CI = 1.09,3.91). Conclusion Higher serum vitamin B12 concentrations,but not serum folate concentrations,were associated with lower odds of childhood obesity.Children and adolescents with high levels of vitamin B12 and folate were less likely to be obese.