A novel kind of asymmetric blend membranes with superfine chitosan powder (SCP) and biomedical polyurethane was prepared by immersion precipitation phase inversion method. Effects of different SCP content on the morphology and properties of the blend membranes were investigated. The result showed that SCP content had little influence on the cross-section structure of the blend membranes, and the cross-section presented a cellular structure. WAXD results revealed that the aggregated structure of SCP remained. With an increment of SCP content, the pore diameter and porosities of blend membranes increased firstly, and then decreased. While, the water absorption rate and water vapor transmission rate were improved remarkably with increasing SCP content. The mechanical testing results indicated that with an increment of SCP ratio, mechanical properties presented a descending trend, whereas all blend membranes exhibited the good elasticity.