In this study we investigated the use of a microbial fuel cell (MFC) to abioticlly cathodic decolorization of a model azo dye, Methyl Orange (MO). Experimental results showed that electricity could be continuously generated the MO-fed MFC and MO was successfully decolorized in the cathode. The decolorization rate was highly dependent on the catholyte pH. When pH was varied from 3.0 to 9.0, the k value in relation to MO degradation decreased from 0.298 to 0.016 μmol min-1, and the maximum power density decreased from 34.77 to 1.51 mW m-2. Sulfanilic acid and N,N-dimethyl-p-phenylenediamine were identified as the decolorization products of MO by HPLC-MS.