The effects of the temperature and fine particles of Fe2O3 upon methyl methacrylate (MMA) thermal polymerization in low density polyethylene (LDPE) matrix were investigated. The MMA mass increment in the composite matrix is a temperature dependent process. It reaches values 10 folds higher at 90 degrees C compared to the mass increment at 60 degrees C. The apparent polymerization rate is dependent of Fe2O3 concentration reaching a maximum at 0.17-0.26 % of Fe2O3 in the composite. The thermal process is catalysed by Fe2O3.