Physically crosslinked hydrogels composed of 80% poly(vinyl alcohol)(PVA) and 20% gelatin were prepared by freeze-thaw treatment in the dimethyl sulfoxide(DMSO) aqueous solution,and the solvent sensitivity of transparency of the hydrogels was studied.It is found that when the composite hydrogels are periodically immersed in distilled water and DMSO aqueous solution,the light transmittances of the hydrogels periodically change in the solvent-exchanging process.With the increase of DMSO concentration,the response rate of light transmittances of the hydrogels increases.XRD results indicate that the construction of crystalline regions in hydrogels are reversible for PVA/gelatin hydrogels in water and DMSO solution,and the crystalline degree decreases with the increase of water content in the hydrogels.The crystalline structure transformation and solvent-induced phase separation may be responsible for the solvent sensitivity of the PVA/gelatin hydrogels.