Fourier transform near-infrared spectroscopy (FT-NIR) was used to determine the dioctyl phthalate (DOP) plasticizer content in polyvinyl chloride (PVC). The FT-NIR spectra for PVC plates were collected in the reflectance mode using the Integrating Sphere module. Data was collected for PVC films using the transmittance mode. Partial Least Squares (PLS) methods were developed for the measurement of DOP in these materials. The results of this study showed that FT-NIR spectroscopy is a suitable technique for the measurement of polymer composition.