China has the third largest area of marshland in the world. Due to the effects of human activities, marshland in China has been widely converted to built-up land (BL) and cultivated land (CL) during the past decades. Using satellite measurements of land surface temperature (LST), this study investigated the biophysical effects of marshland loss on LST. The results showed that marshland conversion to BL could increase the LST during both the daytime and nighttime. Conversion from marshland to CL could increase the daytime LST in most months and nighttime LST in the nongrowing season but decrease the daytime LST from July to September and nighttime LST in the growing season. Conversion from marshland to paddy field and dry farmland had different effects on LST. These complex effects suggest that the biophysical effects of marshland conversions should be considered in evaluating the effects of marshland loss on climate change in China.