The 5-d biochemical oxygen demand (BOD5) test is the most conventional method to determine the concentration of biodegradable organics in wastewater. However, this method is time-consuming and usually requires experience and skill to produce creditable results, which is also not suitable for on-line measurements. This study described a single-chamber mediator-less microbial fuel cell (MFC)-type BOD sensor as an alternative method to BOD5. In such MFC, MnO2 was used as the cathode catalyst instead of Pt and the expensive proton exchange membrane was replaced with the cation exchange membrane. The factors including the external resistance, pH of anolyte, the reaction time and rinse time on BOD sensor were explored, and the results were compared with the values determined by BOD5. The experimental results showed that the optimal conditions are: the external resistance of 12 k omega, pH of 7.0, and the reaction period of 2 h and the rinse time of 2-10 min. The low detection limit is 0.2 mg/L and the precision is 0.33%. This study indicates that MFC-type sensor can be used as a reliable method to determine BOD in wastewater, supported by the good linear correlation between BOD concentration and coulombs generation (regression coefficient, R2 = 0.9992) and the small relative error of 4% between MFC-type sensor and BOD5. Such device provides a low-cost, easy-operated, fast-response, sensitive and reliable method to measure BOD in wastewater, and also is suitable for on-line measurements.