A novel thermosensitive poly(N-vinylisobutyramide)(polyNVIBA) hydrogel was prepared by the copolymerization of N-vinylisobutyramide (NVIBA) with butylene-bis-NVA(B-BNVA) as a crosslinker in a high yield. The swelling transition behavior was examined in comparison with poly (N-isopropylacrylamide) (polyNI-PAAm) hydrogel. The resulting polyNVIBA hydrogel clearly showed a swelling transion in water at ca. 41 degrees C. To control the transition temperature (T-t) of the gel, crosslinked copolymers of NVIBA and N-vinylacetamide (NVA) were prepared and compared with copolymers of N-isopropylacrylamide (NIPAAm) and NVA. The incorporation of NVA led to a higher swelling transition temperature. T-t of poly(NVIBA-co-NVA) gels was almost the same as those in water-soluble poly(NVIBA-co-NVA). The responses for a swelling transition of polyNVIBA and poly(NVIBA-co-NVA) gels were sharp in comparison to polyNIPAAm gels. PolyNVIBA and poly(NVIBA-co-NVA) gels desorbed 98% of water above T-t. The characteristic and the mechanism of the phase transition on the hydrogels were discussed.