Unmodified and hybrid membranes based on Nafion and carbon nanotubes have been synthesized by hot pressing from a mixture of polymer and dopant powders. The water uptake, ionic conductivity under different conditions, and diffusion permeability of the membranes for HCl and methanol solutions have been studied. The hybrid membranes are characterized by high water uptake and proton conductivity in contact with water and low diffusion permeability for hydrochloric acid solution. In contact with water, the conductivity of the samples modified with 1 wt % carbon nanotubes is 0.070 S/cm; the diffusion permeability of a 0.1 M HCl solution is 2.43 x 10(-7) cm(2)/s.