Porous structure of activated carbon (AC) is important for mass transfer and catalyst when AC is used as air-cathode catalyst in microbial fuel cell (MFC). In this work, several carbon samples including two kinds of micropore carbon and mesoporous carbon with different pore sizes are prepared as air-cathode catalyst layer to explore the role of micropore and mesoporous during the process of oxygen reduction reaction (ORR). The catalytic activities of all samples are tested by linear sweep voltammetry (LSV), Tafel and rotating disk electrode (RDE). Besides, these carbon materials are also analyzed by Nitrogen adsorption-desorption isotherms, air permeability test, In situ FTIR and H₂ temperature programmed reduction. Among these carbon samples, AC shows the best ORR performance, because its mesoporous structure is benefit for oxygen pass and micropore structure can promote catalytic activity. Thus, the electrochemical performance of activated carbon contribute to the own functions of micropore and mesoporous.