Nanosized SSZ-13 zeolite was synthesized by traditional hydrothermal method using N,N,N-trimethyl-1-ad-amantanaminium hydroxide as the structure-directing agent (SDA). The influence of different preparative conditions of nanosized SSZ-13 was investigated systematically. The synthetic zeolites were characterized by X-ray powder diffraction (XRD), nitrogen physisorption, and scanning electron microscopy (SEM). By means of the self-assembled method, the thin SSZ-13/polyvinyl alcohol nanocomposite membranes were obtained by incorporating the nanosized SSZ-13 zeolite into the polymeric precursor (polyvinyl alcohol (PVA)). The permeation properties of pure CO2 and CH4 through the mixed matrix membranes (MMMs) were measured. The results showed that the highly crystalline SSZ-13 zeolite in a dispersed nanocrys-tal form with a controllable particle size of 100 nm could be hydrothermally synthesized by optimizing the synthetic param-eters and the selectivity of CO2/CH4 of the MMMs could reach a value of 40 by changing the amount of nanosized SSZ-13 zeolite.