Display omitted •ZnO/g-C3N4 were successfully synthesized using facile hydrothermal method.•ZnO/g-C3N4 nanocomposites were synthesized and the effect of g-C3N4 on NO2, sensing was investigated.•30 % - g-C3N4 shows enhanced response rate 1463 % (10 ppm NO2) at 180 °C.•Gas sensing mechanism of ZnO/g-C3N4 nanocomposites were discussed. In this study, ZnO/g-C3N4 nanocomposites were synthesized using facile hydrothermal method by varying the concentration of g-C3N4 in 10 %, 30 % and 50 % weight percentage. The prepared nanocomposite samples were studied by various characterization techniques for morphological, structural, and elemental confirmation. The pristine ZnO microspheres show 229 % response towards 10 ppm NO2, whereas 30 % - g-C3N4 loaded ZnO nanocomposite shows drastic improvement in response rate around 1463 % (10 ppm NO2) at an operating temperature of 180 °C with rapid response and recovery time of 72 s and 145 s. The improved hybrid nanocomposite performance can be attributed due to the effective interface formation, increased surface area and enhanced gas adsorption active sites.