A novel manganese-polypyrrole-carbon nanotube (Mn-PPY-CNT) composite is synthesized and demonstrated as an efficient and stable cathode catalyst for oxygen reduction reaction (ORR) in air-cathode microbial fuel cells (MFCs). The Mn-PPY-CNT composite is prepared by solvothermal method and comprehensively characterized. Subsequently, electro-catalytic capability of this novel catalyst in neutral electrolyte has been investigated by cyclic voltammetry, showing that Mn-PPY-CNT can catalyze ORR in neutral medium with quite good activity, possibly due to manganese-nitrogen (Mn-N) active sites. To further verify catalytic capability of the Mn-PPY-CNT composite, it has been utilized as the cathode catalyst in air-cathode MFCs. It has been found that Mn-PPY-CNT-based MFCs yield efficient and stable performance with maximum power density of 169 mW m(-2) at the loading of 1 mg cm(-2), and 213 mW m(-2) at the loading of 2 mg cm(-2), comparable to MFCs with the benchmark platinum/carbon black (Pt/C) catalyst. Furthermore, the catalyst shows good long-term stability which is essential for MFC study. This is the first study regarding the manganese-heterocycle polymer composite as a new ORR catalyst, and it has successfully demonstrated that using cheap Mn-PPY-CNT catalyst instead of Pt/C could improve the feasibility of scaling up MFCs for practical applications. (C) 2012 Elsevier B.V. All rights reserved.