Barrier membranes for guided bone regeneration (GBR) were prepared by a solvent casting method using solutions of poly(L-lactic acid) (PLLA) and chitosan. PLLA and PLLA/chitosan membranes were treated with ammonia gas plasma. PLLA/chitosan membranes were successfully fabricated, and the surface of the PLLA/chitosan membrane was clearly modified by NH3 plasma treatment according to attenuated total reflectance (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) analyses. Additionally, water contact angle testing indicated that the hydrophilicity of these membranes was significantly increased. MG-63 cells were cultured on each type of membrane, and cell viability was examined using an MTT assay. After one week of culturing, MG-63 cells were more abundant on PLLA/chitosan membranes than on PLLA membranes. The cell viability of PLLA/chitosan membranes with plasma treatment was significantly higher than that of PLLA membranes. These results suggest that this plasma-treated membrane is suitable for GBR and is a promising source of bioactive membrane material for bone regeneration.