We prepared ZrO₂–ZnO heterojunction composites by a simple hydrothermal method as materials sensitive to isopropanol gas. The 5% ZrO₂–ZnO sample presented a uniform rod-like structure. The optimum operating temperature, sensitivity and response/recovery times were measured to investigate the response of ZrO₂–ZnO composites to isopropanol. The sensor based on 5% ZrO₂–ZnO composites at an optimum temperature of 260 °C had a response to 100 ppm isopropanol of up to 172.46, which was about 3.6 times higher than that of pure ZnO. The sensor also exhibited fast response and recovery times of 5 s and 11 s, respectively. The gas-sensitive properties can be attributed to the rod-like structure, heterojunction structure and catalytic activity of ZrO₂. These results would contribute in expanding the application of ZrO₂ in gas sensors.