The chitosan biopolymer can be used as a proton-conducting membrane in proton-exchange membrane fuel cell. In the forms that they have normally obtained and tested, chitosan membranes typically show poor performance in conduction of protons, requiring modifications in the structure of the biopolymer or blending with other polymers to increase its proton conductivity. The present work investigates the individual properties of chitosan and relates them to the proton conductivity performance of membranes composed of this polymer. Evaluation was made of the effects of variables such as the degree of deacetylation (DD) and the molar mass (Mv) of chitosan membranes without addition of any other polymer. The DD and Mv values of the chitosan used to produce membranes determined the proton conduction, with lower DD and higher Mv resulting in higher conductivity. The thicker membranes presented greater crystallinity, with conductivity between 2.0x10(-4) and 1.8x10(-3)Scm(-1). The characteristic stages of degradation of the chitosan membranes were in the ranges 200 to 300 degrees C and 500 to 600 degrees C, indicating good thermal stability of the material.