PURPOSE The purpose of this study was to analyze the level and characteristics of physical activity (sedentary, light, and MVPA) of high school students according to physical education (PE) class (DWPE: days with PE class, DNPE: days with no PE class) and sex.METHODS Data were collected on 147 students (65 male and 82 female) from four high schools in Seoul city, and physical activity was measured using a three-dimensional accelerometer. The collected physical activity data were input into SPSS 25.0, and the descriptive analysis and two-way ANOVA according to PE class and sex were performed.RESULTS The descriptive statistical analysis showed that 31% (40.7% male and 23.4% female) of participants met the recommended physical activity durations (MVPA of 60 min/day). In the two-way ANOVA, sedentary activity, light activity, and MVPA showed statistically significant main and interaction effects according to PE class and sex. According to the results of the interaction effect analysis, the gap in physical activity between DWPE and DNPE was large in male students. For male students, light activity and MVPA significantly increased on the day of the PE class, and sedentary activity significantly decreased. However, for female students, DWPE and DNPE did not differ significantly in all levels of physical activity.CONCLUSIONS In conclusion, the level of physical activity of Korean high school students was relatively low, and the effect of daily-life physical activity in the PE class was limited to male students. Accordingly, an alternative should be introduced to increase the physical activity of female high-school students through PE classes.