Tremella-like delta-MnO2 (T-MnO2), mixed tremella and short belt-like alpha-MnO2 (M-MnO2), and long belt-like alpha-MnO2 (B-MnO2) are prepared hydrothermally by varying the reaction ratios of KMnO4 to MnSO4. Of the three morphologies, B-MnO2 produces the highest oxygen reduction reaction (ORR) activity in alkaline media. Interestingly, the highest ORR activity do not correlate with the highest BET total surface area of M-MnO2, but rather with the lowest surface area of B-MnO2. XPS analysis shows that B-MnO2 contains the highest ratio of surface Mn(III):Mn(IV), followed by M-MnO2 and T-MnO2. The results suggest a corresponding higher oxygen vacancy density would exist on the alpha-MnO2 crystal form of nanobelts, which thus provides a possible mechanistic basis for their higher ORR activity. (C) 2015 Elsevier B.V. All rights reserved.