Objective To evaluate trends of overweight and obesity prevalence between 1996 and 2007 in Yi farmers and Yi migrants.Methods An Yi migrant study was conducted in Liangshan Yi Autonomous Prefecture,Sichuan Province,China from 1996 to 2007.Data were collected with identical methods,including standardized questionnaire and body measurements.Results Age- and sex-specific body mass index (BMI) significantly increased from 20.02 in 1996 to 22.36 in 2007,among Yi farmers,which was significantly different from those among Yi migrants (23.67 in 2007 and 20.90 in 1996) (P＜0.05).Prevalence of obesity rose from 1.21％ in 1996 to 4.55 ％ in 2007 (OR=1.15,P＜0.001) in Yi migrants,while that in Yi farmers from none in 1996 to 0.12 ％ in 2007 (P＞0.05).Prevalence of overweight rose significantly to 26.24 ％ in 2007 from 17.24 ％ in 1996 (OR=1.06,P＜0.001) in Yi migrants,while that in Yi farmers from 1.29 ％ in 1996 to 4.45 ％ in 2007 (OR=1.14,P＜0.001).Yi migrants appeared to have a 5.52-fold higher risk on developing overweight and obesity than Yi farmers have.Conclusion The Yi migrants had a steeper increase of overweight with year and consequently caused more obesity.Change in lifestyle may contribute most likely to higher prevalence of overweight and obesity in Yi migrants.