The purpose of this study is to determine the prevalence of overweight and obesity and its relationship with physical activity in male students aged between 12 and 17 in Rasht. At first cluster sampling was done randomly and some of the schools were selected by their geographical situation and then some students from different classes were tested. The mean and standard deviation of age, height, weight, percent of body fat, fat weight and lean body mass were 14.52±1.2 (yrs), 161±6.12 (cm), 52.58±14.9 (kg), 16.4±89 (percent),9.8±8 (kg), 43.4±10.5 (kg) respectively. To determine the overweight and obesity prevalence the cut - off, BMI was used and 95% BMI and more was considered as obesity, 85-95% BMI as overweight, 15-85% BMI as optimal body weight and less than 15% BMI as under weight. The subjects also completed Baeck questionnaire of habitual activity. Finally, statistic analysis was applied using Pearson correlation coefficient, and following results was considered: Prevalence of overweight and obesity was 10.9% and 6.5% in male students respectively. Prevalence of optimal body weight and under weight was 52.8% and 29.9% in male students respectively. There was a significant relationship between prevalence of overweight and physical activity (P≤0.05). There was a significant relationship between prevalence of obesity and physical activity (P≤0.05). There was not a significant relationship between BMI and physical activity.