The thermal behaviour of activated carbons obtained from peat and modified with poly(acrylic acid) - PAA films was examined. Additionally, the effect of anionic surfactant - sodium dodecyl sulfate (SDS) presence in the adsorption layer was determined. Three samples of activated carbons were analyzed: (1) sample N - obtained by pyrolysis of peat followed by steam activation, (2) sample N9C - obtained by physical activation of sample N with carbon dioxide and (3) sample N9K - obtained by chemical activation of sample N with potassium carbonate. TG, DTG and DSC coupled with FTIR and QMS spectrometry enable not only specification of thermal stability of examined systems, but also determination of main gaseous products of their thermal decomposition. The obtained results indicate that polymer/surfactant adsorption influences significantly the thermal degradation of used carbon materials.