Objective: To analyze the associations of physical activity with overweight/obesity, depressive symptoms, and their co-occurrence among junior and senior high school students, so as to provide reference for optimizing physical activity intervention strategies and promoting healthy lifestyles. Methods: From March to November 2023, a cross sectional survey was conducted among 90 457 junior and senior high school students aged 11-18 years in Zhejiang Province using a stratified cluster random sampling method. Data on physical activity and dietary behavior were collected through questionnaires, height and weight were measured. Depressive symptoms were assessed using the Center for Epidemiologic Studies Depression Scale (CES-D). The Chi-square test was used to examine differences, and Logistic regression was applied to evaluate the associations of physical activity characteristics with overweight/obesity, depressive symptoms, and their co-occurrence. Additionally, the effectiveness of physical activity performed on rest days versus work days was examined. Results: The prevalence of overweight/obesity, depressive symptoms, and their co-occurrence among junior and senior high school students were 25.1%, 27.9%, and 6.7%, respectively, with significant sex differences ( χ 2=2 005.3, 587.7, 99.6, all P <0.01). Logistic regression analysis showed that students with insufficient physical activity had a higher risk of overweight/obesity compared with those with sufficient physical activity ( OR=1.12, 95%CI=1.06-1.17, P <0.01). Comparing to students who exercised 0-1 day per week, those who exercised 5-7 days per week were associated with a reduced risk of overweight/obesity and depressive symptoms ( OR=0.93, 95%CI =0.90-0.97; OR=0.95, 95%CI =0.91-0.99, both P <0.05). When total activity volume and frequency were held constant, students with sufficient rest day physical activity had lower risks of overweight/obesity, depressive symptoms, and their co-occurrence than those with insufficient rest day activity (all P < 0.01). Conclusions Sufficient amount of physical activity and higher frequency of rest day physical activity are significantly associated with lower risks of overweight/obesity, depressive symptoms, and their co-occurrence in adolescents. Physical activity performed on rest days may confer greater health benefits than activity performed on work days.