The degradation effects of benzoylferrocene (BF) on poly(ethylene glycol) (PEG) and poly(methyl methacrylate) (PMMA) were investigated using MALDI-MS. It is supposed that the release of free radicals in solution by BF plays a key role in the decomposition of PEG and PMMA. MALDI-MS combined with examination of the degradation by BF could be applied to the analysis of synthetic polymer structures containing the PEG and PMMA chain.