This study investigates the urban heat island (UHI) effect in 32 major Chinese cities using MODIS data from 2003 to 2012. The UHI effect decays exponentially toward rural areas, with a "temperature cliff" between urban and rural regions. The footprint of the UHI effect (FP), including urban areas, was found to be 2.3 to 3.9 times the urban size, with significant spatiotemporal variability. Ignoring the FP can lead to underestimation of UHI intensity and even reverse the direction of UHI estimates in some cities. The FP was largest at night, reaching up to 3.9 times the urban area, and smaller during the day (2.3 times). The FP varied significantly across cities and seasons, with larger values in colder or drier regions. The FP was also influenced by background climate, vegetation activity, and land use patterns. The study highlights the importance of considering city-specific FP when assessing urbanization effects on local climate. The results provide new insights into the characteristics of the UHI effect and emphasize the need for accurate FP estimation in future studies. The FP was found to be larger in summer than in winter, and the day-night difference was attributed to varying mechanisms underlying the UHI effect. The study also shows that the UHI effect can be underestimated if the FP is ignored, and that the direction of UHI estimates may be reversed in some cases. The findings have important implications for understanding and mitigating the impacts of urbanization on climate and environment.This study investigates the urban heat island (UHI) effect in 32 major Chinese cities using MODIS data from 2003 to 2012. The UHI effect decays exponentially toward rural areas, with a "temperature cliff" between urban and rural regions. The footprint of the UHI effect (FP), including urban areas, was found to be 2.3 to 3.9 times the urban size, with significant spatiotemporal variability. Ignoring the FP can lead to underestimation of UHI intensity and even reverse the direction of UHI estimates in some cities. The FP was largest at night, reaching up to 3.9 times the urban area, and smaller during the day (2.3 times). The FP varied significantly across cities and seasons, with larger values in colder or drier regions. The FP was also influenced by background climate, vegetation activity, and land use patterns. The study highlights the importance of considering city-specific FP when assessing urbanization effects on local climate. The results provide new insights into the characteristics of the UHI effect and emphasize the need for accurate FP estimation in future studies. The FP was found to be larger in summer than in winter, and the day-night difference was attributed to varying mechanisms underlying the UHI effect. The study also shows that the UHI effect can be underestimated if the FP is ignored, and that the direction of UHI estimates may be reversed in some cases. The findings have important implications for understanding and mitigating the impacts of urbanization on climate and environment.