Oxygen reduction reaction plays an important role in improving the performance of microbial fuel cell (MFC). MnO2:rGO with different ratios (100:0), (85:15), (75:25), and (60:40) were used as cathode electro-catalyst, and performance analysis was done to find the optimum ratio. The isolated bacteria with new strain, Bacillus subtilis subspecies spizizenii strain No NBRC 101239 (ACCESSION no NR_112686) was used for the first time as a biocatalyst. MnO2 and MnO2:rGO were synthesized by reflux method and were characterized by X-ray diffractometer, thermogravimetric analysis, Fourier transform infrared spectroscopy, scanning electron microscopy, and laser Raman spectroscopy. It was found that the MFC with ratio (75:25) showed higher performance with maximum power density 32.5 mW/m(2) compared to 6.76 mW/m(2) (85:15), 3.79 mW/m(2) (100:0), and 3 mW/m(2) (60:40).