Hybrid membrane materials on the basis of sulfonated polynaphthaleneimide doped with ceria have been synthesized, and their ionic conductivity has been investigated. The conditions for membrane synthesis with different dopant contents have been determined. Ceria doping leads to a decrease in the ionexchange capacity of membranes and an increase in their ion conductivity upon contact with water. After 7% ceria doping, the ionic conductivity of the initial membrane (1.9 x 10(-2) Omega(-1) cm(-1)) increases up to 3.0 x 10(-2) Omega(-1) cm(-1).