Polyacrylic acid (PAA) is degraded in an aqueous medium with Fenton's reagent. At long reaction times, 17 hours at 60°C, acrylic acid polymer suffer decarboxylation with Fenton's reagent. At the end of the degradation process, the polymeric product has physically changed, becoming an amorphous smooth material. It has lost the initial crystallinity. The DSC data indicates polymer degradation with weight loss of volatile products as a consequence of the decarboxylation. Macroradial formation that experiments intercrossing reactions, forming a more stable structure, this is indicating by the lower weight loss percentage. At the same time, PAA with Fenton's reagent at 5 and 17 hours, presents an exoterm at 418 °C and 416 °C, respectively. This indicates volatile products degradation and macrostructure loose of the polymer