The thermal behavior of several chitosan/alginate /drug microparticle formulations containing ciprofloxacin, ibuprofen, ketoprofen or tannic acid was investigated by thermogravimetry in inert atmosphere in the temperature range of 25 - 900 degrees C. The chemical composition and the method used for drug incorporation influenced the thermal stability of the products. It was found that the entrapment of the drug in chitosan, alginate or chitosan/alginate complex modifies the degradation mechanism introducing new degradation steps by comparison with raw polymers. The activation energy for the main degradation step is also changed.