Physical inactivity is a growing issue in Chinese youth, but parks can facilitate traditional and non-traditional forms of physical activity for little to no cost. Despite this opportunity, very little is known regarding park use among Chinese youth. The purpose of this study was to conduct a cross-sectional observational study of park usage and physical activity of youth in municipal parks in Nanchang, China. Data were collected in June of 2014 in eight parks across Nanchang, Jiangxi a large city in southeast China. Physical activity was measured by a modified version of System for Observing Play and Recreation in Communities. Ordered hierarchic generalized linear models were estimated using a logit link function. The influence of the park was estimated using random effects, with fixed effects and park, environmental, and park user characteristics. Youth were most often seen active in the afternoon, on weekends, and during cooler times (≤ 29 °C). Paradoxically, more children were active when air quality was poorer. Older boys were more active than younger boys, but no differences were observed in girls. More children were seen active in unstructured play compared to structured activities. The results suggest parks are an important setting for physical activity among Chinese youth, and that unstructured activities can play an important role in promoting greater youth physical activity.