A detailed comprehensive investigation has been made to unequivocally analyse the end groups of a vinyl polyperoxide polymer namely, poly(methylmethacrylate peroxide), PMMAP, using Fast Atom Bombardment Mass Spectrometric (FABMS) technique. Further evidence to FABMS analysis has been sought from IR spectroscopic analysis on the same polymer. It has been found that PMMAP contains both hydroxyl and hydroperoxide end groups which has been explained by the chain transfer reaction of growing chain with the degradation product of PMMAP.