In this study, N-vinylcaprolactam was polymerized via gamma irradiation in the solid state. The polymerization was carried out at room temperature both under vacuum and open to atmosphere. The polymerization mechanism showed auto acceleration and the rate of polymerization was higher in the presence of oxygen. Complete conversion was obtained under vacuum conditions and 90% conversion was obtained in the case of polymerization open to atmosphere. The polymers were characterized by FTIR, NMR, DSC, TGA, GPC, X-ray diffraction and mass spectrometry tests. FTIR and NMR results showed that polymerization proceeded through the vinyl groups and caprolactam is pendant group. DSC results showed that the polymer obtained could be polymerized further or crosslinked by heat treatment. The Tg value for the polymer obtained from radiation induced polymerization was about 135C and increased to 174.6C after thermal treatment. Molecular weights of some polymer samples were measured by GPC. X-ray diffraction studies showed that the monomer structure was retained up to about 86% conversion of monomer to polymer. The chain structure of the polymer was confirmed by mass spectroscopy results.