An IR spectroscopy technique was developed to study the plasticizer migration from polymer compositions to the air environment. The applicability of the method was exemplified for filled PVC compositions plasticized with di-n-butyl phthalate. Values for the effective diffusion coefficient D of the plasticizer were calculated from the spectroscopic data. An increase in the chalk content in a PVC composition leads to a monotonic increase in D, whereas kaolin-filled compositions exhibit a more complex behavior. The observed pattern of changes in D with varying the filler content was correlated with the competing interaction of components in the system.