The compatibilizing efficiency for PET/PP blends was examined using tensile testing, dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC) and scanning electron microscopy of crycrofractured surfaces before and after etching. Compatibilizers used were maleic anhydride modified, PP (PP-g-MA), LLDPE (LLDPE-g-MA) and hydrogenated SBS block copolymer (SEBS-g-MA). Large deformation behavior of aged blends indicated that SEBS-g-MA performed best by far. However, addition of a thermoplastic polyolefin alloy (TPO), PP/ethylene-propylene copolymer, increased the compatibilizing efficiency of PP-g-MA to a level comparable to that of SEBS-g MA. Improved efficiency of SEBS-g-MA and PP-g-MA + TPO compared to PP-g-MA or LLDPE-g-MA is attributed to better emulsification of the former at the interface, reduced migration of PP-g-MA into the PP phase and retardation of PET crystallization in the presence of the elastomeric additive. In addition, the elastomeric compatibilizers absorb more efficiently, the stresses developed at the PET/PP interface.