Abstract: Objective To study the nutritional status,cognition on self-evaluated weight and unhealthy weight control behaviors among adolescent students in Tianjin city and to provide evidences for effective intervention.Methods A self-administered anonymous questionnaire survey was conducted among 8 194 students of 11-26 years old recruited with stratified cluster random sampling from 36 middle schools and 6 universities in Tianjin city in 2013.Results The rate of emaciation,overweight,and obesity among the students were 11.53%,11.62,and 6.52%,respectively.The rate of overweight and obesity were obviously higher among the boy students than among the girl students (15.59% vs.8.19% and 9.16% vs.4.23%).The highest rate of obesity (13.88%)was reported by the students aged 12 years and the lowest rate of overweight and obesity (8.72% and 2.78%)were reported by the college students.A higher obesity rate (7.71%)was reported by the students from regions with better economic condition and a lower obesity rate was reported by the students from nuclear families.The results of the multivariate conditional logistic regression analysis showed that gender,whether being a boarding student,consumption of soft drinks,dessert eating behavior,fast food eating behavior,familial economic condition,and whether playing video games were influence factors of overweight and obesity among the students (P<0.05 for all).Of all the students,51.76% had biased cognition on their weight;of the students with emaciation and normal weight,8.04% and 37.64% perceived their weight as heavier or very heavy;whereas,of the students with overweight and obesity,16.91% and 26.77% had incorrect cognition on their weight,with a significant difference (χ²=3 061.461,P=0.01).In the survey,there were 22.80% of the students reporting having physical exercise to lose or control weight during the previous 30 days and 21.19% reporting taking unhealthy activities to lose weight;the reported prevalence of unhealthy behavior for losing weight was positively related to the increment of weight (χ²_trend=3 061.461,P=0.01).Conclusion Emaciation,overweight and obesity are prevalent at a relative high level concurrently and there are biased cognition on self- perceived weight and unhealthy behavior for losing weight among adolescent students in Tianjin.