PLGA nanofibers were prepared by an electrospinning method (mean diameter, 340 nm) and treated with plasma in the presence of either oxygen or ammonia gas to modify the surface of the nanofibers. The surface hydrophilicity of electrospun PLGA nanofibers was greatly increased by plasma treatment, which was confirmed by contact angle measurement. XPS analysis demonstrates that the number of polar groups on the surface of PLGA nanofibers after plasma treatment was increased, and this was considered to contribute to the enhanced surface hydrophilicity of the nanofibers. This approach to controlling the surface properties and structures of nanofibers could be useful in the design and tailoring of novel synthetic extracellular matrices for tissue engineering applications.