The effects of cisplatin and its trans-isomer transplatin on the thermokinetics of actin polymerization have been studied by measurement with an MS-80 Calvet calorimeter (Setaram, France). The power-time curves show that transplatin inhibits the normal association of actin, promotes the abnormal association of actin even at lower concentrations; and induces the depolymerization of actin polymer in the G/F system at higher concentrations. However, cisplatin, at lower concentrations, mainly inhibits the polymerization of actin; at higher concentrations, it induces the crosslinking and depolymerization of actin polymer in the G/F system.