This study examined the effect of positively charged gold nanoparticles ((+)AuNPs) on the enhancement of methylene blue (MB) degradation in microbial fuel cell (MFC) cathode. The maximum electricity production of 36.56 mW/m2 and complete MB degradation were achieved simultaneously. The MFC performance and MB degradation are strictly dependent on cathodic conditions, such as N2 bubbling, air bubbling and addition of H2O2. MB was reduced rapidly under anaerobic condition, whereas complete oxidative mineralization of MB occurred in the presence of dissolved oxygen (DO) or H2O2. (+)AuNPs enhanced the electricity generation in the MFCs involving MB degradation owing to its electron relay effect. Presence of both (+)AuNPs and H2O2 produced largest enhancement in MB degradation. After 5 h, almost all MB (98%) and COD (chemical oxygen demand) (96%) had been removed in the presence of (+)AuNPs, whereas only 57.4% of MB and 40% of COD had been removed in the absence of (+)AuNPs.