Chitin/poly(glycidyl methacrylate) (PGMA) composites were synthesized via bulk polymerization in a gel state of chitin impregnated with reactive GMA monomer. The thermal transition behaviour and phase structure of the chitin/PGMA composites were characterized by differential scanning calorimetry (d.s.c.), dynamic mechanical analysis (d.m.a.), and solid-state C-13 n.m.r. spectroscopy. For compositions rich in PGMA (chitin less than or similar to 20 wt%), it was revealed by d.s.c. and d.m.a. that the polymerized samples gave a T-g value higher than that of PGMA homopolymer, and the magnitude of lowering of their modulus E’ in the glass transition region became extremely small, compared with the corresponding E’-drop noted for PGMA alone. To interpret these observations, it was reasonably assumed that an original network structure of chitin gels was sufficiently perpetuated into the polymerized bulks, accompanied by the formation of an IPN-like organization. Through the measurements of proton spin-lattice relaxation times in the n.m.r. study, the scale of homogeneous mixing in the TPN type of polymer composites was evaluated. The result suggested that the chitin and PGMA components were mixed mutually on a scale of a few nanometres in those composites.