The composites of SnO₂ have attracted much interest in the last few years due to their excellent sensing properties. A series of composites were prepared with two-dimensional (2D) g-C₃N₄ nanosheet modified SnO₂ by a simple hydrothermal method in this work. The as-prepared composites were characterized by the techniques of powder X-ray diffraction (XRD), thermogravimetric analysis (TG), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), N₂ sorption and X-ray photoelectron spectroscopy (XPS). The gas sensing measurement results indicated that the sensor based on g-C₃N₄/SnO₂ composite showed high sensitivity and excellent selectivity for detection of ethanol vapor. At 500 ppm of ethanol vapor, the response value (R_a/R_g) of 5 wt% 2D g-C₃N₄ modified SnO₂ was 240 at 300 °C. Therefore, the g-C₃N₄/SnO₂ composites have a great potential ethanol gas sensing application.