In this paper, the behavior of micro-scale effect in a micro direct methanol fuel cell ( DMFC) is investigated through both simulations and experiments. A model is built to describe the methanol distribution in the diffusion layer with different feature sizes. In addition, the dynamic movement of a single CO2 bubble is also simulated to study the two-phase characteristics in the micro channels with various aspect ratios. Furthermore, a metal-based transparent DMFC with the active area of 0.64 cm(2) is designed and fabricated to evaluate the two-phase flow characteristic as well as the corresponding cell performance. The experimental results reveal that when the feature size scales down to 0.6 mm and 0.4 mm, the peak power density of 27.1 mW cm(-2) and 26.3 mW cm(-2) are achieved at room temperature. Finally, the effect of adjusting channel aspect ratio is experimentally investigated to improve the inner convection transport and the cell output, and the results are well in agreement with the simulation. (c) 2016 Elsevier Ltd. All rights reserved.