The process of volatilization of dioctyl phthalate (DOP) plasticizer from plasticized poly(vinyl chloride) (PVC) folies was studied by the method of isothermal thermogravimetry in the temperature range of 120-150 degrees C. The investigated samples contained 10.15 to 37.11 wt% of DOP. The rate constants of the process of plasticizer volatilization were calculated and the dependence of rate constant on the initial concentration of plasticizer in plasticized PVC and on temperature were mathematically defined. The concentration dependence is expressed by parameters k(0) and q. The activation energy of the process was calculated from the exponential dependence of the rate constant of volatilization on temperature.