[en] The g-C₃N₄ nanosheets decorated three-dimensional (3D) hierarchical flower-like SnO₂ nanocomposites were synthesized via a facile hydrothermal method by using the g-C₃N₄ and SnCl₂·2H₂O as the precursors. The structure and morphology of the as-synthesized samples were characterized by the X-ray powder diffraction (XRD), electron microscopy (FESEM and TEM), N₂ sorption, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectrometer (FT-IR) techniques. It is supposed that g-C₃N₄ nanosheets act as a template in the hydrothermal process, accelerating the preferential growth of SnO₂ nanocrystals and preventing the agglomeration of the SnO₂ nanoparticles. The gas sensing performances of the as-synthesized samples to ethanol vapor were tested, and the response of the sensor based on 3 wt.% g-C₃N₄ decorated SnO₂ composite to 500 ppm ethanol vapor was 360 at 300 °C, which was much higher than that of pure flower-like SnO₂ based sensor. The improved ethanol gas sensing property is proposed to relate to the good conductivity of g-C₃N₄, high specific surface area and interactions between g-C₃N₄ and SnO₂. - Highlights: • Flower-like SnO₂/g-C₃N₄ composite has been developed. • Flower-like SnO₂ were coupled by a lamellar structure 2D g-C₃N₄. • The as-prepared composites possess much higher response of ethanol than pure SnO₂. • Flower-like SnO₂/g-C₃N₄ composite will be an ideal candidate for ethanol gas sensor application.