NIPAAm hydrogels were prepared by γ-irradiation to various doses. The temperature responsive and the swelling behaviors of the hydrogels were monitored by DSC and gravimetric measurements. Mechanical properties of the hydrogels were characterized by rheology measurements. It is found that the microstructure of hydrogel changes dramatically with dose. At lower doses the formed hydrogel is inhomogeneous with many branched long chains in the network. The incomplete molecular network resulted in a limited swelling and lower strength of the hydrogel. At higher doses

the over cross-linked network prevents water permeation and therefore inhibits swelling of the hydrogel. It is found that under present experimental conditions

the hydrogel prepared at a dose of 30kGy shows the best swelling and mechanical properties.