This study evaluates whether changes in weight among school-aged youth in California due to the COVID-19 lockdown vary by social constructs of race/ethnicity and associated social factors.Including 160,472 youth ages 5-17 years enrolled at Kaiser Permanente Southern California, mixed effects models stratified by age group were fitted to estimate changes in distance from the median body mass index (BMI)-for-age from 3/2020 to 1/2021 (lockdown) compared to the same period prepandemic.Excess pandemic weight gain was higher among Black and Hispanic youth 5-17 years than among white and Asian youth; this difference was most pronounced in those ages 5-11 years. In youth 5-11 years, the distance from the median BMI-for-age increased by 1.72 kg/mThe COVID-19 pandemic lockdown led to a gain of excess body weight, particularly for Black and Hispanic youth; this weight gain varied by social factors associated with race and ethnicity. This article is protected by copyright. All rights reserved.