Graft-copolymerization of methyl methacrylate (MMA) and acrylonitrile (AN) onto CTMP fibers using Fe2+-H2O2redox system was investigated. The proof of grafting was performed by means of FT-IR and gravimetric methods. Analyses of IR spectra of samples after mercerization, xanthation, ion exchange and of samples with different polymer loadings, together with chemical reactions were performed. The variation of the characteristic IR band absorption intensity of MMA (the C˭O groups stretching at 1731 cm−1) and of AN (the nitrile stretching at 2244 cm−1) vs the percent of grafting can be used as calibration curves for quantitative determination. It appears also from the IR spectra analyses, that some of the mechanisms suggested for graft-copolymerization are of very small significance.