Air-conditioning use behaviors of the people in mixed-mode buildings have a significant impact on building energy. A one-year field investigation was conducted in mixed-mode residential buildings mainly on the elderly in the Hot Summer and Cold Winter Region. Climate parameters, air-conditioning usage rates, turning-on time, and indoor set-point temperatures were continuously monitored and recorded. The results show that the periods of the elderly using air conditioners in the living rooms, dining rooms, and bedrooms were different in summer and winter. In summer, the indoor set-point temperatures of living rooms and dining rooms were both mostly within 26~28°C, and those of bedrooms mainly varied within 25~29°C. The most frequent set-point temperature of the three rooms was 27.5°C. In the winter, the indoor set-point temperatures of all rooms were similar, and the most frequently selected one was 20.5°C. In summer, the outdoor tolerance temperatures of the elderly were about 31°C and 26°C in the daytime and night, respectively. In winter, the outdoor tolerance temperature of the elderly was about 12 °C and 8°C in the daytime and night, respectively. Besides, this study established the logistic regression models between air-conditioning use rates and outdoor temperatures, normal-distributed models of air-conditioning use rates over time, as well as the models of indoor set-point temperature distribution. This study provides a reference for researches on air-conditioning use behaviors in mixed-mode residential buildings.