A series of C₃N₄/CuGaO₂ composites were synthesized by facile hydrothermal method. The prepared samples were characterized by XRD, SEM, TEM, and XPS. The gas sensing properties of the C₃N₄/CuGaO₂ composites were investigated. Results demonstrate that the gas sensor based on C₃N₄/CuGaO₂-0.3 composite (molar ratio of C₃N₄ to CuGaO₂ is 0.3:1) shows better sensing performance to toluene than CuGaO₂ sensor does. Compared with the operating temperature of CuGaO₂ sensor (140 °C), the optimal working temperature of C₃N₄/CuGaO₂-0.3 composite sensor is only 25 °C, the response to 100 μL/L toluene gas reaches 28, and the detection limit is as low as 0.01 μL/L. The response time and recovery time for the detection of 100 μL/L toluene vapor are 114.2 and 27.4 s, respectively. Moreover, the C₃N₄/CuGaO₂-0.3 composite sensor also exhibits excellent long-term stability, good repeatability, and extraordinary humidity resistance for toluene detection.