Abstract The preparation of sulfonated polybenzimidazole (sPBI) by the grafting of (4‐bromomethyl) benzenesulfonate onto polybenzimidazole (PBI) has been investigated. The methanol permeability and proton conductivity of PBI and sPBI have been studied, and the effects of methanol concentration and temperature on the methanol permeability of PBI and sPBI membranes are discussed. The results showed that the PBI membrane is a good methanol barrier. Methanol permeability in this membrane decreases with increasing methanol concentration and increases with increasing temperature. The temperature‐dependence of methanol permeability of PBI and sPBI membranes is of the ‘Arrhenius type’. Methanol permeation of sPBI is less sensitive to temperature than that of PBI. However, sPBI is a poorer methanol barrier when compared to PBI. Methanol permeability in sPBI membranes increases with increasing methanol concentration and temperature. The proton conductivity of sPBI is 4.69 × 10 −4 S cm −1 at room temperature in the hydrated state. The DC conductivity of sPBI–H 3 PO 4 increases with increasing temperature. Proton transport in sPBI–H 3 PO 4 is less sensitive to temperature than that in PBI–H 3 PO 4 . Copyright © 2004 Society of Chemical Industry