In this paper, the synthesis, characterization and sensing properties of SmFeO3/ZnO nanocomposite synthesized by the thermal treatment method, is reported. The morphological and microstructural characteristics of the synthesized composite nanopowders and single SmFeO3 and ZnO components, were analyzed by Scanning Electron Microscopy-Electron Dispersive X-ray (SEM-EDX), X-ray diffraction (XRD), Fourier Transform-Infrared (FT-IR) spectroscopy and Photoluminscence (PL). Characterization analyses revealed that SmFeO3/ZnO nanocomposite sample is composed of individual SmFeO3 nanoparticles in the orthorhombic phase and ZnO in the wurzite phase. However, emission characteristics in the photoluminescence spectra suggest a high interaction degree between the components of composite. The gas-sensing characteristics of the nanopowders were evaluated in the detection of acetone at low concentration in air. The very high acetone sensitivities of SmFeO3/ZnO nanocomposite sensor was discussed in the framework of the p-n junctions model.