Introduction: Childhood obesity has become a public health problem all around the world. Childhood obesity has serious comorbidities, which can affect almost every system in the body and can also persist into adulthood. There are multiple factors affective in etiology, but lifestyle habits (eating behaviors and physical activity) are especially more important. During the coronavirus disease-19 (COVID-19) pandemic, the lifestyle of obese children has changed by necessity. The aim of this study was to investigate the effects of the COVID-19 pandemic on diet, exercise habits, and metabolic control in obese children. Method: Forty-nine obese children between the ages of 6 and 18 years, who applied to the pediatric endocrinology department between November 2020 and April 2021, were included in this study. Metabolic parameters (glucose, lipid, insulin, thyroid hormones, body mass index and cortisol level) were analyzed retrospectively and children's nutritional habits and physical activity durations during the pandemic period were evaluated. Results: Our data showed that body mass index was increased during pandemic (p<0.01). A statistically significant increase was found in glucose, insulin, low density lipoprotein, and triglyceride levels (p<0.05). High density lipoprotein and T4 levels were decreased (p<0.01). No statistically significant increase was found in the levels of thyroid stimulating hormone (p=0.13) and cortisol (p=0.16). This study has been shown that the time spent on physical activity decreased in 40 children (83.6%), while the time spent in front of the screen (computer, telephone etc.) increased in 39 children (79.5%). When we examined the eating habits, it was shown that 36 patients (73.5%) have poor diet (feeding score <0). Conclusion: According to these results, body mass index of obese children were increased and metabolic parameters were changed during the COVID-19 pandemic. Children have become more sedentary, and their eating habits have changed dramatically in this process. [ABSTRACT FROM AUTHOR]