Cellulose/poly(N-vinylpyrrolidone-co-glycidyl methacrylate) (CELL/P(VP-co-GMA)) composites were synthesized via photopolymerization in the gel state of cellulose swollen in a mixture of VP and GMA monomers as reactive impregnant. The cellulose gels were formed from homogeneous solutions in N,N-dimethylacetamide/lithium chloride by coagulation in ethanol, followed by exchange of the coagulant for the monomer mixture. The thermal transition behaviour and phase construction of the (CELL/P(VP-co-GMA) composites obtained in film form over a wide composition range were investigated. For compositions containing less than 20 wt% CELL, it was reasonably assumed that the original network structure of cellulose gels was sufficiently perpetuated into the polymerized bulk. Dynamic mechanical analysis revealed that the lowering of the storage modulus (E’) of the copolymer-rich composites in the glass transition temperature (T-g) region was extremely suppressed, compared with the corresponding E’ drop observed for plain P(VP-co-GMA) samples. The additional treatment of as-polymerized composites with aqueous formic acid or sodium hydroxide solution gave rise to a marked elevation of their T-g values, due to a certain crosslinking reaction in the copolymer constituent. A similar T-g elevation phenomenon was noted in the case where CELL/P(IP-co-GMA) samples were subjected to a prolonged heat treatment at temperatures higher than ca. 175 degrees C. This may be ascribed to the prominence of crosslinking between the cellulose and copolymer components through reaction of GMA epoxides with cellulose hydroxyls.