This study investigates the possible impact of urbanization on the summertime extreme precipitation–temperature (P–T) relationship in East Asia. The local climate in three megacity regions—Guangdong in China, Seoul/Gyeonggi in Korea, and Tokyo in Japan—is particularly examined by analyzing a high-resolution dataset of in situ measurements for the period of 1973–2015. All three megacity regions exhibit statistically significant positive trends in mean and extreme temperature and precipitation; an exception is the seasonal-mean precipitation in Tokyo, which shows no clear long-term trend. When extreme precipitation is binned with respect to temperature, the P–T relationship sharply changes across the breaking point where the maximum precipitation intensity occurs. The breaking point occurs at a higher temperature in the urban areas than in the rural areas, with a stronger extreme precipitation intensity. However, extreme precipitation at relatively cold temperature exhibits an opposite relationship, with a weaker urban precipitation than rural precipitation. This urban–rural contrast in the P–T relationship of extreme precipitation has become more pronounced in the recent decades, with more intense extreme precipitation in the urban areas than in the rural areas at the temperature around the breaking point. This result suggests that rapid urbanization has likely contributed to the intensification of extreme precipitation in East Asian megacities.