A silane coupling agent (SCA) was used as a compatibilizer for polypropylene-poly(ethylene teraphthalate) (PP-PET) blends with 20, 40, 50, and 60% PET compositions by weight. PP-PET mixtures were blended with and without an SCA by a single-screw extruder. The effect of silane modification on the tensile and impact properties of the blends was investigated. The morphology and thermal behavior of the blends were examined with scanning electron microscopy (SEM) and differential scanning calorimetry (DSC), respectively. The presence of the SCA used in this work extensively improved the mechanical properties of the blends. Mechanical properties were found to be highly dependent on the numbers of extrusions. SEM studies showed that substantially different morphology with better adhesion existed when SCA-treated blends were compared to nontreated PP-PET blends. The presence of individual melting temperatures of the polymers in all compositions with no significant T m depression indicated that PET and PP were crystallized separately.