Poly(ethylene terephthalate) (PET) was blended with four different kinds of eo[poly(ethylene terephthalate-p-oxybenzoate)] copolyesters, designated P28, P46, P64, and P82, with the level of copolyester varing from 1 to 15 wt%. All samples were prepared by melt-mixing in a Brabender Plasticorder for 8 min. The crystallization behavior of samples were then studied via DSC. The results indicate that these four copolyesters accelerate the crystallization rate of PET in a manner similar to that of a nucleating agent. The acceleration of the PET crystallization rate was most pronounced in the PET/P28 blends with a maximum level at 10 wt% of P28, and in the PET/P82 blends, at 5 wt% of P82. The melting endotherm onset temperatures and the melting peak widths for the blends are comparable with those of neat PET. These results imply that the stability of PET crystalline phase in the blends does not change by blending. The observed changes in crystallization behavior, however, are explained by the effect of the physical state of the copolyester during PET crystallization as well as the content of the p-oxybenzoate (POB) moiety incorporated into the blends.