Abstract: Semi-interpenetrating network(semi-IPN) hydrogels, poly[NVP-IPN]/PEG were prepared from N-vinyl-2-pyrrolidone(NVP), acrylic acid(AA) and polyethylene glycol(PEG) through free radical polymerization, in which AIBN was used as a free radical initiator and N,N'-methylene bis(acryl-amide)(BIS) as crosslinking agent. In polymer systems as characterized by DSC poly[NVP-AA] and PEG are partially compatible. The hydrogel thereof was pH sensitive due to the carboxyl group in the polymer structure. 5-Fuorouracil(5-FU), an anti cancer drug was choiced for entrapment test of the polymer capsule. The in-vitro release studies were carried out in synthetic gastric and intestinal fluids(SGF and SIF buffer solution) at 37℃. The results showed that with the increase of PEG content in the hydrogel, the corresponding release profile became flatter, release period longer, and the final equilibrium release percentage decreased. Moreover, the drug releasing behavior are affected by the cross-linking degree of the polymer and the medium it contacts with. The drug release profiles for hydrogels with different BIS content were similar in SIF buffer solution, while in SGF buffer solution, the higher degree of cross linking of poly[NVP-AA], the longer the releasing time.