We have investigated a low production cost anhydrous proton conductor consisting of a composite of chitosan, one of the world's discarded materials, and methanediphosphonic acid (MP) having a high proton exchange capacity. This chitosan-200 wt.% MP composite material showed the high proton conductivity of 5 x 10(-3) S cm(-1) at 150 ° C under anhydrous conditions. Additionally, the proton conducting mechanism of the chitosan-MP composite material was due to proton transfer to the proton defect site without the assistance of diffusible vehicle molecules. The utilization of a biopolymer, such as chitosan, for PEMFC technologies is novel and challenging where biological products are usually considered as waste, non-hazardous, and environmentally benign. Especially, the low production cost of the biopolymer is an attractive feature. Anhydrous proton conducting biopolynter composite membranes may have potential not only for PEMFCs operated under anhydrous conditions, but also for bio-electrochemical devices including an implantable battery, bio-sensors, etc. © 2004 Elsevier Ltd. All rights reserved.