Thermal behaviour of tetracycline hydrochloride, oxytetracycline dihydrate, Co(II) and Ni(II) complexes of tetracycline and Zn(II) complexes of some cephalosporin antibiotics, namely cephalexin, cephapirin, cefuroxime, and ceftazidime was studied using thermogravimetric analysis (TG). The TG curves exhibit several thermal events indicating that the thermal decomposition of these compounds are not simple. The kinetic parameters for steps appropriate for kinetic analysis were evaluated making use of the Coats-Redfern equation. During the thermal decomposition of tetracycline hydrochloride anhydrotetracycline was proposed to be formed as an intermediate due to the elimination of water.