gamma-Ray radiation on poly(glucosyloxyethyl methacrylate) [poly(GEMA)] and poly(glucosyloxyethyl acrylate) [poly(GEA)] aqueous solutions without any crosslinkers gives glycoside-bearing hydrogels in a high yield. The degree of the swelling ratios of each obtained hydrogel in water was decreased with an increase in the total radiation dose to each polymer solution. In order to clarify the formation mechanism of obtained poly(GEMA) hydrogel by gamma-ray radiation, the swelling properties of each hydrogel were also compared with those of poly(GEA) under various conditions. Poly(GEMA) in an organic solvent, N,N-dimethylformamide and dimethylsulfoxide, was not gelled by gamma-ray radiation, although poly(GEA) was gelled under these conditions. These results suggest that the radiation formation mechanism of the poly(GEMA) hydrogels is different from that of the poly(GEA) hydrogels. In addition, the radiolysis of water is necessary in order to form the hydrogels for poly(GEMA). Next, we predicted the radiation formation mechanism of the poly(GEMA) hydrogels by the crosslinking between the glucoside moieties in poly(GEMA).