Fuel cells are being developed to overcome the global energy crisis. The objective of this research is to prepare an environmental-friendly and cheap material as the polymer electrolyte membrane. Coconut water was fermented by Acetobacter xylinum to produce nata-de-coco and the phosphorylation was carried out by microwave-assisted reaction. The resulting membranes are characterized by ion exchange capacity, contact angle, proton conductivity, swelling index, methanol permeability, mechanical properties measurement and morphological analysis. At the optimum phosphorylation condition using 17.35 mmol of phosphoric acid, membrane showed a proton conductivity of 1.2 x 10(-2) S/cm and a methanol permeability of 2.3 x 10(-6) cm(2)/s. The tensile strength of the produced membranes increases significantly and the arrangement of the cellulosic fibers are kept well-aligned. It is concluded that a green and sustainable natural resources can be used for preparing electrolyte membrane. (c) 2013 Wiley Periodicals, Inc.