Background:Meeting 24-h movement guidelines by children and adolescents has been associated with improved indicators of health, although it has been under-studied in China. Hence, this study aimed to investigate the prevalence of meeting the 24-h movement guidelines, its correlates, and its relationships with body mass index in children and adolescents in China. Methods:Cross-sectional data from the 2017 Youth Study in China of 114,072 children and adolescents (mean age=13.75 years, 49.18％boys) were used. Meeting 24-h movement guidelines (≥60 min of daily moderate-to-vigorous physical activity, ≤2 h of daily leisure screen time, 9-11 h and 8-10 h nightly sleep duration for 6-13-year-olds and 14-17-year-olds, respectively) and height and weight of all participants were assessed. The prevalence of meeting the 24-h movement guidelines and World Health Organization weight status categories were determined. Generalized linear models were used to determine the correlates of meeting the 24-h movement guidelines and the relationships of meeting the 24-h movement guidelines with overweight (OW) and obesity (OB). Results:Only 5.12％of Chinese children and adolescents met the 24-h movement guidelines, and 22.44％were classified as OW/OB. Older chil-dren and adolescents were less likely to meet the 24-h movement guidelines. Parental education level and family income were positively related to meeting the 24-h movement guidelines. Children and adolescents meeting the 24-h movement guidelines showed lower odds ratios for OW/OB. Compared with participants meeting the 24-h movement guidelines, boys in 4th-6th grades met none of the recommendations (OR=1.22, 95％CI:1.06-1.40), met the screen time recommendation only (OR=1.13, 95％CI:1.01-1.28), met the nightly sleep duration rec-ommendation only (OR=1.14, 95％CI:1.03-1.28), and had significantly higher odds ratios for OW/OB. Similar trends were observed for girls in 4th-6th grades:meeting none of the guidelines (OR=1.35, 95％CI:1.14-1.59), meeting sleep duration guidelines only (OR=1.23, 95％CI:1.08-1.39), and meeting moderate-to-vigorous physical activity+nightly sleep duration guidelines (OR=1.24, 95％CI:1.01-1.54). For girls in 7th-9th grades, the following trend was observed:meeting none of the guidelines (OR=1.30, 95％CI:1.01-1.67). Conclusion:Very few Chinese children and adolescents met the 24-h movement guidelines. Age (negatively correlated), parental education level, and family income (both positively correlated) were correlates of meeting the 24-h movement guidelines. Children and adolescents meeting the 24-h move-ment guidelines were more likely to have lower risks for OW/OB, especially in the youngest age group (Grades 4-6);and girls in the middle age group (Grades 7-9) were also more likely to have lower risks for OW/OB. Further research studies should explore additional correlates and determinants for meeting the 24-h movement guidelines. Also, future studies should use longitudinal or interventional designs to determine the relationships between meeting the 24-h movement guidelines and OW/OB and other health indicators, while taking sex and age differences into account.