Hydrogels based on polyacrylic and polymethacrylic acids were synthesized using two variants of redox initiating systems and three crosslinking agents in various ratios to the monomer. The chemical structure of these hydrogels was extensively studied by Fourier transform infrared (FTIR) spectrometry and Raman spectrometry. These hydrogels were also characterized by other techniques, namely thermo gravimetric analysis (TGA), differential thermal gravimetry, differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). The hydrogel ability to immobilize enzymes through covalent bonds was studied by FTIR and Raman spectrometry and by analyzing the SEM images before and after enzyme immobilization. The enzyme influence on the thermal behavior of the hydrogel biocomposite was investigated by DSC and TGA, too. The methacrylic acid leads to more thermo stable hydrogels formation than acrylic acid. Acrylic and methacrylic hydrogels are able to covalently immobilize enzymes. This is proved by the important changes which occur in the chemical composition, the thermal behavior and the morphology of hydrogels after immobilization stage. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013