This study was conducted to investigate the effects of different temperature treatments on kumquat fruit development and qualities. Kumquat trees were placed in growth chambers at day/night temperatures of 36°C/28°C, 28°C/20°C, and then 20°C/12°C two weeks after the first physiological fruit drop. The results showed that there was a positive correlation between temperature and fruit drop. The total fruit drop rate increased with temperature. The group at 36°C/28°C had the highest total fruit drop rate of 63.7%. High temperature (36°C/28°C) suppressed kumquat fruit growth. With increases in temperature, the lengths and diameters of fruits decreased. Moreover, the kumquat peel color in the 36°C/28°C and 28°C/20°C groups did not change from green to orange. High day/night temperatures (36°C/28°C) during fruit growth stages suppressed fruit growth and could reduce fruit quality. Low day/night temperatures (20°C/12°C) prolonged the fruit development period, increasing fruit size and allowing peel color to change successfully. In order to avoid fruit drop caused by high temperatures at the fruit setting stage, pruning in early February is recommended.