While previous studies mainly focused on low-frequency variabilities of mean or extreme temperature, it remains unclear how the high-frequency variability (HFV) of temperature changes within few days and to what degree local urbanization contributes to these changes. In this study, we examine the changes of temperature HFVs over South China and quantify their urbanization effects. We find that the HFV there shows a discernible spatial dependence with higher values in northern inland and lower in southern coastal regions. The study area has experienced increasing HFV trends since the 1980s, and these trends are especially stronger in highly developed regions, e.g., the Pearl River Delta. We further estimate that urbanization induces additional intensifying effects of 0.06, 0.10, and 0.10 °C/100 yr for HFV at the time scales of 1, 2, and 5 days, respectively, and these urbanization effects contribute to 46.2%, 43.5%, and 37.0% of the total trends of HFV in the urban areas. Our findings are helpful for mitigating the increasing threats of HFV and promoting sustainable development in populated urban areas.