Preparation of membranes from stimuli-responsive polymers, copolymers, and polymer-additive mixtures is an important approach in the design of responsive membranes. N-isopropylacrylamide(NIPPAm) was dispersed in polyurethane(PU) solution, crosslinked with N,N’-methylene bisacrylamide(BIS) and then cast in bathes to get a thermosensitive microporous film. The ratio of NIPAAm with BIS amount and the cast medium were varied. The structure, surface and cross-section images of polyurethane/poly(N-isopropylacrylamide) (PU/PNIPPAm) semi- interpenetrating networks (semi-IPNs) were characterized by FT-IR and SEM. The swelling behavior of pure PU films and PU/PNIPPAm semi-IPNs were compared. The results showed that incorporation of PNIPPAm had great effect on the structure and swelling behavior of composite films. This approach enables fabrication of membranes with the desired pore structure.