Objectives: This study is a descriptive research study to identify factors affecting physical activity of Korean adolescents after COVID-19. Method: The data were from the 18th(2022) online survey on adolescent health behavior was used, and data from a total of 51,850 people attending middle and high school were used in the final analysis. Data were analyzed using frequency, weighted percentage, χ²test, and logistic regression analysis using the complex sample analysis module of the SPSS/WIN 24.0 program. Result: As a result of the study, 23.8% of adolescents had good physical activity, and most adolescents had poor physical activity, Factors affecting adolescents’ physical activity include general characteristics such as gender(p<.001), grade(p<.001), academic performance(p=.014), economic status(p<.001), and residence type (p=.001), and mental health-related factors included perceived stress(p<.001), depression(p<.001), and loneliness experience(p=.029). Conclusion: After COVID-19 epidemic, Adolescent health promotion strategies are needed to promote mental health management and increase physical activity, including reducing stress and depression among Korean Adolescent.