The effect of low-temperature surface-wave plasma treatment with various gases on surface modi. cation of chitosan was investigated using the surface-wave plasma. Chitosan is a nontoxic, biocompatible and biodegradable polymer. It is thought that an increase in amino groups, a key constituent of chitosan molecules, will be useful for biomedical applications, such as improvement of blood clotting properties, drug delivery system, prodrug using derivatization and so on. In this study, therefore, we have focused on the amino group introduction on chitosan surface by using Ar, O-2, NH3 and NH3-He mixed gas plasmas. The experimental results of X-ray photoelectron spectroscopy measurements showed that N/C atomic ratio increased from 6.8% to 14.7% after NH3 plasma treatment. With O-2 plasma treatment, the surface roughness of chitosan film was significantly modified from 1.96 nm to 14.6 nm. The blood clotting time of the sample treated by NH3 and He plasma with O-2 pretreatment was reduced to 55.2% of that of untreated one. (C) 2008 Elsevier B. V. All rights reserved.