Poly(ethylene terephthalate) (PET) was blended with a co[poly(ethylene terephthalate-p-oxybenzoate)] (POB-PET) copolyester which is a liquid crystalline polymer consisting of p-oxybenzoate and ethylene terephthalate units in a 40/60 mol ratio (P46). The level of P46 liquid crystalline polymer varies from 10 to 50 wt %. All the blends were prepared by melt-mixing in a Brabender Plasticorder at 275 degrees C for different times. The thermal and crystallization behaviors of blends depend on the blending time and the composition of blends, viz., the content of the p-oxybenzoate (POB) moiety incorporated into the blends. The interchange reactions detected by proton NMR analysis occur during the processing at a greater level if the blending time increases. These interchange reactions hinder the crystallization processes of PET and result in a decrease of the melting point, the heat of fusion, crystallization temperature, and the heat of crystallization of the original PET. The effects of the interchange reaction on thermal and crystallization behaviors of the blends may be attributed to the insertion of the rigid POB units into the soft PET chain.