Crosslinked sulfonated PSU blend membranes have been produced via a new crosslinking process. The blends have been obtained from mixing of PSU Udel(TM) Na-sulfonate and PSU Udel(TM) Li-sulfinate in N-methyl pyrrolidone. The membranes have been crosslinked by S-alkylation of PSU sulfinate groups with dihalogenoalkanes The membranes produced via this process have been characterized in terms of ion-exchange capacity, electric resistance, swelling, ion-permselectivity. In addition, the thermal stability of the membranes has been determined by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), and FTIR-spectra of the prepolymers and of the crosslinked blend membranes have been recorded. The new crosslinking procedure shows following advantages : (i) the preparative effort for crosslinking is very low; (ii) the properties of the crosslinked membranes are reproducible; (iii) the crosslinking proceeds with a high yield when applying suitable dihalogenoalkanes or other crosslinkers which are capable to S-alkylate the sulfinate group. The properties of the crosslinked PSU blend membranes are : (i) low electrical resistance at high IEC＇s; (ii) low swelling rate in practical temperature ranges from 20-70 degrees C; (iii) excellent hydrolysis stability; (iv) excellent thermal stability.