China has a vast territory with a variety of climates. Residents living in different climate zones are exposed to different indoor thermal environments in their homes and thus may have various thermal comfort levels. This study conducted a one-year campaign in 157 residential apartments in 12 cities across five climate zones in China by means of indoor thermal environment monitoring and online questionnaires in bedrooms. The study found that the severe cold (SC) and cold (C) climate regions had a warm and dry winter with median air temperature and relative humidity of around 23 ^oC and 25%, respectively. In summer, the cold climate region had the highest indoor air temperature among all regions. In terms of thermal sensation, more than 85% of residents voted in the middle three categories (slightly cool, neutral, and slightly warm), indicating an overall satisfactory thermal environment in Chinese residential buildings. However, residents in the hot summer and cold winter (HSCW) region reported the highest percentage of “cold” votes (18%) in winter, while those in the cold climate region reported the highest percentage of “hot” votes (18%) in summer. A “seasonal effect” was observed, by which the thermal sensation and clothing insulation in a particular season followed the general air temperature level of that season. The findings of this study are expected to contribute to the design and control of a thermally comfortable environment in residential buildings.