In this work, we report on a novel one-pot hydrothermal synthesis of bismuth (Bi)-doped SnO2/rGO nanocomposites. The composite structures, surface morphologies, chemical compositions, optical properties and crystal defects were characterized by XRD, SEM, TEM, BET, FTIR, Raman, XPS, EPR, PL and UV–vis techniques, and the gas sensing properties to benzene (C6H6) were investigated thoroughly by the temperature-controlled CGS-1TP gas sensing test system. Compared with that of the pure SnO2 and rGO/SnO2, the Bi-doped SnO2/rGO presented largely enhanced gas sensing properties to benzene. Its high gas response, fast response-recovery characteristic, good stability and selectivity made Bi-doped SnO2/rGO an ideal sensing material to detect benzene. However, the as-prepared Bi-doped SnO2/rGO based sensor also showed degenerative gas sensing performance at high humidity. The enhanced gas sensing performances of Bi-doped SnO2/rGO could be attributed to the large specific surface area of the composite structure, the unique rGO-SnO2 heterojunctions, the narrowed band gap, and enormous oxygen vacancies. This novel Bi-doped SnO2/rGO composite promises to provide an essential gas sensing material for the detection of benzene.