The influence of optimal ultraviolet irradiation of Nafion membranes in enhancing proton conductivity and performance of passive micro-direct methanol fuel cells with silicon micro-flow channels is investigated for the first time. Initially, Nafion membranes are irradiated with different doses of ultraviolet radiation ranging within 0-400 mJ cm(-2) and their water uptake, swelling-ratios, porosity, and proton conductivities are measured using standard procedure. Results show that there is an enhancement in proton conductivity with an optimal dose of 198 mJ cm(-2) ultraviolet radiation. This enhancement is due to optimum photo-crosslinking of -SO3H species resulting in maximum pore-size which facilitates enhanced proton-hopping from one -SO3H site to another in the hydrophilic channel. Nafion membranes with three different thicknesses (50 mu m, 90 mu m and 183 mu m) are irradiated with ultraviolet radiation with 198 mJ cm(-2) dose and passive micro-direct methanol fuel cells are assembled with irradiated Nafion proton exchange membranes. The polarization plots are obtained for the assembled devices. Results show an enhancement of power density of devices nearly by a factor of 1.2-1.5 with optimally irradiated membranes indicating that optimum dose of ultraviolet irradiation of Nafion membranes is an effective technique for power enhancement of proton exchange membrane fuel cells which use fuels like methanol, ethanol and hydrogen. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.