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(VP- co-GMA) samples were subjected to a prolonged heat treatment at temperatures higher than ca. 175°C. This may be ascribed to the prominence of crosslinking between the cellulose and copolymer components through reaction of GMA epoxides with cellulose hydroxyls.