This study examines the global distribution and stock of soil organic carbon (SOC) in urban greenspaces, which are growing with global urbanization. By analyzing 420 observations from 257 cities in 52 countries, the authors find that surface SOC density in urban greenspaces increases significantly at higher latitudes and decreases with higher mean annual temperature, stronger temperature and precipitation seasonality, and lower urban greenness index. Using a random forest model, they estimate an average SOC density of 55.2 Mg C ha\(^{-1}\) (51.9–58.6 Mg C ha\(^{-1}\)) and a total SOC stock of 1.46 Pg C (1.37–1.54 Pg C) in global urban greenspaces. The findings provide a comprehensive assessment of SOC in these areas and offer a baseline for future urban soil carbon assessments under continuing urbanization. The study highlights the importance of climatic factors, such as temperature and precipitation, in controlling SOC density, while vegetation conditions and urban management also play significant roles. The results suggest that urban greening efforts can potentially increase topsoil C sequestration in established urban areas, but future climate change may pose risks to SOC stocks in high-latitude urban greenspaces.This study examines the global distribution and stock of soil organic carbon (SOC) in urban greenspaces, which are growing with global urbanization. By analyzing 420 observations from 257 cities in 52 countries, the authors find that surface SOC density in urban greenspaces increases significantly at higher latitudes and decreases with higher mean annual temperature, stronger temperature and precipitation seasonality, and lower urban greenness index. Using a random forest model, they estimate an average SOC density of 55.2 Mg C ha\(^{-1}\) (51.9–58.6 Mg C ha\(^{-1}\)) and a total SOC stock of 1.46 Pg C (1.37–1.54 Pg C) in global urban greenspaces. The findings provide a comprehensive assessment of SOC in these areas and offer a baseline for future urban soil carbon assessments under continuing urbanization. The study highlights the importance of climatic factors, such as temperature and precipitation, in controlling SOC density, while vegetation conditions and urban management also play significant roles. The results suggest that urban greening efforts can potentially increase topsoil C sequestration in established urban areas, but future climate change may pose risks to SOC stocks in high-latitude urban greenspaces.