Poly(ethylene octene) (POE), maleic anhydride grafted poly(ethylene octene) (mPOE), and a,mixture of POE and mPOE were added to poly(butylene tetephthalate) (PBT) to prepare PBT/POE (20 wi % POE), PBT/mPOE (20 wt % mPOE), and PBT/mPOE/POE (10 wt %. mPOE and 10 wt % POE) blends with an extruder. The melting behavior of neat PBT and its blends nonisothermally crystallized from the melt was investigated with differential scanning calorimetry (DSC). Subsequent DSC scans exhibited two melting endotherms (T-mI and T-mII). T-mI was attributed to the melting of the crystals grown by normal primary crystallization, and T-mII was due to the melting of the more perfect crystals after reorganization during the DSC heating scan. The better dispersed second phases and higher cooling rate made the crystals that grew in normal primary crystallization less perfect and relatively prone to be organized during the DSC scan. The effects of POE and mPOE on the nonisothermal crystallization process were. delineated, by kinetic models. The dispersed phase hindered the crystallization; however, the well-dispersed phases of an even smaller size enhanced crystallization because of the higher nucleation density. The nucleation parameter, estimated from the modified Lauritzen-Hoffman equation, showed the same results. (C) 2007 Wiley Periodicals, Inc.