Blended cellulose/chitin membranes with various mixing ratios were successfully prepared by a co-solvent method from cellulose carbamate (CC) and chitin (CT) in an alkali/urea aqueous system. The blended solutions were characterized by rheological measurements. Blending CT with CC effectively enhanced the thermal stability of the as-obtained CT solution. The prepared membranes were characterized by FTIR, 13C NMR, XRD, TG, XPS, SEM, AFM, Raman, and tensile tests. CC and CT were homogeneously distributed in the blended membranes which clearly demonstrates the compatibility between the two polymers. The blended membrane with 20 wt% CT exhibited outstanding thermal stability and mechanical properties. Furthermore, all membranes were subjected to pervaporation tests. The blended membranes demonstrated excellent separation performance in pervaporation of water (6 wt%)-butanol (94 wt%) mixtures. Among all the membranes, the blended membrane with 20 wt% CT loading demonstrated the best pervaporation performance, achieving a permeation flux of 414.4 ± 40.1 g m−3 h−1 and a separation factor of 798.9 ± 10.5. In addition, the membranes showed stable separation performance over 3 days of continuous pervaporation. Therefore, this study provides guidance and reference for the design of high-efficiency pervaporation polymer blended membranes.