NiFeSi mixed oxide catalysts were prepared using the surfactant-assisted co-precipitation method to remove the CO which may be present in the fuel before entering the fuel cell, and the catalysts were calcined at two different temperatures in order to determine the effect of the calcination temperature on the characteristic properties. Catalysts were prepared in four different NiO, Fe2O3 and SiO2 weight ratios. The X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), N-2 physisorption, high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM) and energy-dispersive X-ray (EDS) analysis were used to characterize the catalysts. CO methanation was done using 1% CO, 50% H-2 and the remainder He feed condition. The reaction temperature varied between the 125 degrees C and 375 degrees C. X-ray diffraction analysis showed that catalysts composed of NiO, Fe2O3 and SiO2 crystal phases. Catalysts calcined at 500 degrees C gave highest surface areas and their structures are composed of spherical particles on the surface. Low surface areas were obtained in catalysts calcined at 700 degrees C due to structural deterioration, such as small pores breaking down and combining to form large pores. Due to the increase in calcination temperature from 500 degrees C to 700 degrees C, the rod-like particles were formed from spherical particles. Activity studies were done over the catalysts calcined at 500 degrees C since they have highest surface area values. Between the catalysts, 0.8/0.2/1 NiFeSi mixed oxide catalyst gave the highest activity which gave 50% CO conversion at 188 degrees C and 100% CO conversion at T > 275 degrees C.