This study aimed to investigate the effects of home confinement as a result of lockdown on physical the activity (physical activity and dietary behaviors), and their determinants, on Turkey high school students (14-18 years). Methods: A total of 490 students (mean age = 16.40 ± 1.75) participated in the study. An online questionnaire consisting of sociodemographic data, nutritional behavior and physical activity habits was applied to the participants. He compared physical activity level (PA), dietary behavior (DB), and sitting time before and during lockdown. Results: BMI (kg/m2) has increased compared to before Covid-19, Physical activity levels of high school students decreased (p < 0.001), increased more their sitting time during lockdown (0.041***), eating habits changed (0.310***). Conclusion: Our data show that high school students are affected by isolation and lockdown and exhibit negative behavioral changes.