CrAPSO-34 crystals were synthesized by conventional hydrothermal method with Cr isomorphously substituted into their structures. CrAPSO-34 membranes were prepared by microwave-assisted heating on porous alpha-Al2O3 substrates seeded with CrAPSO-34 crystals. These membranes were characterized by SEM, EDX, XRD, FT-IR, and UV-Vis techniques. The dense CrAPSO-34 membrane with a thickness of about 2.5 mu m was formed after secondary growth. FT-IR and UV-Vis provided direct evidence for Cr substitution into the CHA zeolite membrane structure. The defect size distribution of CrAPSO-34 membranes indicated that non-zeolitic pores were negligible, which was further conformed by the result of single-gas permeances for CrAPSO-34 membrane versus kinetic diameter of the permeating molecule. The separation performance of CrAPSO-34 membranes for equimolar CO2/CH4 gas mixtures was presented. These membranes displayed CO2 permeances as high as 7.9 x 10(-7) mol/m(2) s Pa with CO2/CH4 separation selectivities in the 152-156 range at 302 K and a pressure drop of 138 kPa.