A series of cross-linked proton exchange membranes with the ion exchange capacities (IECs) of 0.70 - 1.52 meq/g have been prepared via the reaction of the anhydride-terminated sulfonated polyimide oligomers (SPI-3, SPI-5 and SPI-7, here the figure refers to the averaged block length) and the polybenzimidazole with pendant amino groups (H2N-PBI) in dimethylsulfoxide (DMSO) during the membrane cast process. The prepared cross-linked membranes showed high tensile strength (55 - 80 MPa) and good water stability (> 2 months in deionized water at 100 °C). Fenton’s test revealed that all the cross-linked membranes displayed significantly better radical oxidative stability than the corresponding pure SPIs. This is attributed to the presence of the highly oxidative-stable PBI component in the cross-linked membranes. The proton conductivities of the cross-linked membranes increased with increasing temperature and relative humidity. The cross-linked membrane prepared from the longest oligomer (SPI-7) displayed the highest proton conductivity which is comparable to that of Nafion 117.