This work describes a relatively easy transient method for estimating the methanol crossover rate of proton exchange membrane (PEM) and the efficiency of direct methanol fuel cell (DMFC). The method uses a DMFC that includes an anode and cathode chamber; a PEM arranged between the anode and the cathode, and a small motor fan connected to the DMFC. An aqueous solution of methanol is fed into the anode chamber while the motor fan is operated in a loading state, allowing the methanol to crossover to the cathode. The methanol crossover rate of PEM and the efficiency of DMFC are obtained by the current transient analysis. (c) 2006 Elsevier B.V. All rights reserved.