The PDMS-chitosan composite membranes were prepared by addition of 0.02∼0.60 wt% chitosan to PDMS.In order to investigate the characteristics of these membranes, we used the analytical methods such as SEM and TGA. Gaspermeation experiments was performed in 30℃, 4 kg/cm², the permeability and selectivity of H₂ and N₂ according to contentchange in composite membrane were investigated. The permeability of H₂ and N₂ for the PDMS-chitosan compositemembranes increased when 0∼0.20 wt% chitosan was added, and then decreased at higher wt% as chitosan contentincreased. The selectivity (H₂/N₂) of PDMS-chitosan composite membranes decreased when 0∼0.20 wt% chitosan was added,and then increased as chitosan content increased. In the case of PDMS-chitosan in which chitosan was inserted toPDMS, thermal stability of PDMS was enhanced. Based on SEM observation, as the chitosan content within PDMS increased,the surface of the composite membranes became coarse and began to form holes.