The evaluation of complex mass spectra requires effective data processing and visualization methods. The recently invented data mining procedure, the mass-remainder analysis (MARA), was further developed for use in the mass spectrometry of polymer blends containing copolymers. MARA is based on the calculation of the mass remainder after dividing by the exact mass of a base unit, e.g., the repeat unit of a polymer. Our improved method, the multistep mass-remainder analysis (M-MARA), performs sequential calculations of the remainders. The keys of the method are the selection of the base units and visualization by MR3 versus m/z and/or MR2 versus MR1 plots, where MR, is the mass remainder of the ith step. The proposed method eliminates the periodicities present in a complex system and therefore provides highly simplified plots. The effectiveness of the M-MARA method was demonstrated by the analysis of polylactide/polycaprolactone and various ethylene oxide/propylene oxide copolymer samples.