An IR spectroscopy technique was developed to study the plasticizer migration from polymer compositions to the air environment. Applicability of the method was exemplified for the filled PVC compositions plasticized with di-n-butyl-o-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 the varying filler content was correlated with competing interaction of components in the system.