Abstract：    The purpose of this study was to investigate the effects of socioeconomic status (SES) and tutoring time of junior high school students on their physical activity (PA) after school and on weekends using an accelerometer. Participants included a total of 295 students (156 boys and 139 girls) from three junior high schools in the Taipei Area. The junior high schools were targeted and two classes from each grade of each school were selected for the study. Their moderate to vigorous physical activity (MVPA) was objectively measured for seven days; the family's SES and tutoring time with weekdays after-school and weekend MVPA data were also assessed. Results showed that (1) male students had significantly longer average duration of MVPA after school and during weekends than female students; (2) the SES showed a non-significant main effect on the average times of MVPA after school and during weekends; and (3) there was a statistically significant association between SES and tutoring time, i.e., the high SES students had longer tutoring times. We conclude that this study finds a gender effect in that adolescent boys and girls tend to exhibit different intensities of PA. The reasons that adolescent girls may have engaged in less PA include body image issues and gender roles. When adolescents are making decisions about engaging in PA, their decisions may be affected by SES but may also be driven by individual factors. Lastly, students choose to participate in private tutoring to improve academic achievement and pursue a more prestigious diploma. In this study, adolescent boys and girls only engage in MVPA for 12 to 18 minutes per day, which is far below the recommended MVPA level. This indicates that the PA engagement of adolescents in Taiwan needs to be improved. (Full text)