A fast responsive, thermosensitive poly(N-isopropylacrylamide) (PNIPA) hydrogel was obtained after cold-treatment of a swollen, untreated PNIPA hydrogel at low temperature for 24 h. After this treatment, the PNIPA hydrogel exhibits a faster deswelling rate than untreated PNIPA hydogel. This property is probably due to an enhancement of the regularity of macromolecular arrangement during the freezing process.