OBJECTIVES: To investigate temporal trends in childhood and adolescent overweight/obesity in Jiangsu Province, China, evaluating the effects of age, period, and birth cohort. DESIGN: Cross-sectional study. SAMPLE: Participants were 210,168 students aged 6-17 years from the five waves of the consecutive cross-sectional Jiangsu provincial surveillance project in 2017-2021. MEASUREMENTS: Overweight/obesity was assessed according to the sex- and age-specific body mass index. We used age-period-cohort (APC) analysis to explore the temporal trends of overweight/obesity and to estimate the effects of age, period, and birth cohort on the prevalence. RESULTS: The overall prevalence of overweight/obesity has increased from 32.08% to 38.60% between 2017 and 2021. The 6-9-year-old group and the 10-13-year-old group were significantly associated with a higher risk of overweight/obesity, in contrast to 14-17-year-olds. The pandemic was also significantly associated with a much higher risk. The cohort 2000-2003 was associated with higher risk, and such association continued until the cohort 2012-2015, denoting a significantly lower risk. CONCLUSIONS: Despite an increasing trend in the prevalence of overweight/obesity, especially during the COVID-19 pandemic, the latest cohort effect was significantly associated with a lower risk. We recommend continuous efforts on preventive interventions and more research about prevalence trends.