Poly(acryloyl-L-proline-methyl ester) (1) has optically active side chain, and constitutes thermoresponsive hydrogels upon crosslinking. In this study, we have prepared uncrosslinked polymer of 1 with a 10-kGy irradiation dose of gamma -ray. For this polymer, 1, variable temperature circular dichroism (CD) and H-1: NMR spectra have been studied in the range of 0-30 degreesC. The intense CD spectrum at 0 degreesC suggests that the side chains in 1 have an ordered orientation. The CD intensity decreases gradually with increasing temperature. The decreased intensity of CD spectra indicates that; the disordering occurs for the side-chain orientation. The CD band shape changes discontinuously at 20 degreesC. In the H-1 NMR spectra, signals disappear above 20 degreesC. These spectral change at 20 degreesC indicate that the phase transition occurs at around 20 degreesC from swollen to shrunken phase. Even after the phase transition, the CD spectra are still changing with isochromic point at 212 nm. It appears that the side-chain conformation is still changing from one state to the other state in the shrunken phase polymers.