A good mixing of reactants is important for non-premixed combustion in miniature combustors. In this paper, mixings of methane and oxygen in Y-shaped mesoscale combustors with and without porous media were compared numerically. The results show that when there is no porous media in the horizontal channel, the mixing becomes worse with the decrease of the included angle between two inlets, or with the increase of inlet velocity. The reason is that for the case without porous media, the dominant mixing mechanism is molecular diffusion under concentration gradients. In contrast, for the case with porous media, due to the mass dispersion effect which becomes more significant with the decrease of channel width, satisfactory mixing can always be attained in the Y-shaped mesoscale combustor. Moreover, fairly good mixing can still be achieved in the horizontal channel of shorter length. All these demonstrate that the porous media greatly promotes the methane/oxygen mixing in the Y-shaped mesoscale combustor, which is beneficial for flame stabilization. Meanwhile, the combustor dimension can be further scaled down because good mixing is possible in the channel with even smaller included angle and shorter length. This is very important for the application of miniature power generation system. (C) 2014 Elsevier B.V. All rights reserved.