For direct methanol fuel cell, the proton conducting membrane based on semi-interpenetrating polymer networks (IPNs) of Nation and crosslinked poly(AMPS) was prepared and characterized. The modification of Nation with crosslinked poly(AMPS) such as hydrocarbon polymer changed the state of water in membranes. Without a significant increase of the membrane resistance, the semi-IPNs demonstrated a reduction of the methanol permeability, comparing to the native Nation. And the maximum power density of AMPS60 increased as much as 22.2% compared with Nafion. (C) 2004 Elsevier Ltd. All rights reserved.