Radiation induced solid state polymerization of methacrylamide was carried out, opened to atmosphere and under vacuum conditions at room temperature. The white colored powder polymers obtained were insoluble in most common organic solvents such as carbon tetrachloride, dimethysulfoxide, acetone, etc. The polymers were characterized by IR, direct pyrolysis mass spectrometer (DP-MS), XRD, TGA, and DSC methods. The mechanism of the polymerization was elucidated from these results. There were no definite effects of oxygen on the polymerization mechanism. The limiting diffusion of oxygen into the material is due to the close packing of monomer molecules. Polymerization proceeds on the monomerpolymer interface by the opening of the vinyl bond. The polymer obtained was amorphous and did not give a melting peak in DSC thermogram. From the experimental data, it was shown that the polymer gave a side group cyclization upon thermal treatment.