Abstarct: Gas sensor is a type of transducer that it can detect gas molecules and generates an electrical signal according to gas concentration and gas type. Among the solid state gas sensors, semiconducting gas sensors play important role in detection of species gases due to their low cost, small size, easy usage and suitable stability. Recent research have demonstrated that ferrites could be good materials for semiconducting gas sensor. Nickel Ferrite (NiFe2O4) is a mextal oxide semiconductor which has been utilized as gas sensor. In this project, Nickel Ferrite nanoparticles doped with Cobalt (0 – 0/3) were synthesized by Microwave assisted combustion method and their gas sensing to acetone gas were investigated. The structure and surface morphology of the samples were studied using X-ray diffraction (XRD) and Filed Emission Scanning Electron Microscope (FESEM). XRD spectra indicate the formation of spinel phase. In this work, the effects of different parameters such as annealing temperature, the dopant concentration and the acetone gas concentration were studied. The results showed that the gas sensitivity of the all samples reduce with increase in annealing temperature. The maximum response achieved in sample with %5 Cobalt doping at the work temperature of 300C.