Crosslinked chitosan (CS) membrane with sub-micrometer porous structure was prepared by extraction of polyethylene glycol (PEG) from CS/PEG semi-IPN membrane. The content of PEG and the crosslinking agent has significant effects on the pore structure, swellability, and mechanical properties of the membranes. The membrane is pH sensitive, exhibiting reversibility and rapid response in swelling to pH changes. The swelling ratio oscillated between ca. 120 and 220 when pH was varied between 3.2 and 11. It also has good mechanical strength both in dry and swollen state. Thus, it was expected as potential candidate for biomedical use as environmental pH condition altered. (C) 2004 Elsevier B.V. All rights reserved.