The characterization and gas transport properties (i.e., permeability, diffusivity, and solubility) of poly(lactic acid) (PLA) blend membranes were systematically investigated. PLA blends had a glass transition temperature of 60 degrees C, a crystallization temperature of 116 degrees C, and a melting temperature of 149 degrees C. The membrane density increased with increasing crystallinity. In contrast, the fractional free volume determined using a group contribution method of van Krevelen decreased with increasing crystallinity. The ranking of the gas permeability at 35 degrees C in all PLA blend membranes used in this study was hydrogen > carbon dioxide > oxygen > nitrogen. In general, as the crystallinity in a polymer membrane increases, gas permeability decreases. Interestingly, the permeability coefficient of some gases in the PLA blend membrane with higher crystallinity was larger than that with lower crystallinity. This result suggests that the size and distribution of free volume in the crystalline PLA blend membrane are different from those in other crystalline polymer membrane.