Bio-electricity generation by Microbial Fuel Cell (MFC) has gained considerable attention due to its integration with wastewater treatment such as Palm Oil Mill Effluent (POME). Investigation into pH effect and determination of optimal pH value ranges growth for acidogenic, acetogenic and methanogenic by natural mixed culture electroactive bacteria (exoelectrogens) growth in original non-Deoxygenated Mixed POME (nDMP) and Deoxygenated Mixed POME (DMP) in MFC was carried out. Current generation, power generation and maximum power were also monitored. Experimental results show that exoelectrogens in nDMP with pH 6.8 yielded the highest current generation of 61.51 mAm^-2 and maximum power of 17.63 mWm^-2. Overall, nDMP substrates with 3 pH ranges (5.5, 6.8 and 8.0) showed equal potential to generate power that is higher than DMP substrates. Comparison carried out for inter DMP substrates demonstrated that DMP with pH 6.8 and DMP with pH 8.0 showed equal potential to generate power, but not for DMP with pH 5.5. Subsequently, nDMP with pH 6.8 and nDMP with pH 8.0 showed equal potential for higher maximum power compared to nDMP with pH 5.5 and DMP substrates. This finding indicates that mixed microbial communities in DMP substrate are dominant with obligate anaerobic exoelectrogens bacteria which have less capability to generate electricity compared to nDMP substrate that was dominated by the aerotolerant and/or facultative anaerobic exoelectrogens bacteria.