In this study, melt-crystallization behaviors of poly(butylene terephthalate) (PBT) composites including different types of inorganic fillers were investigated. Composite samples having 5 wt % of fillers were prepared by melt processing in a twin screw extruder using commercial grades of calcite (CA), halloysite (HL), and organo-montmorillonite (OM) as filler. Depending on the filler type and geometry, crystallization kinetics of the samples was studied by differential scanning calorimetry (DSC) methods. Effect of filler type on the nonisothermal melt-crystallization kinetics of the PBT was analyzed with various kinetic models, namely, the Ozawa, Avrami modified by Jeziorny and Liu-Mo. Crystallization activation energies of the samples were also determined by the Kissinger, Takhor, and Augis-Bennett models. From the kinetics study, it was found that the melt-crystallization rates of the samples including CA and HL-nanotube were higher than PBT at a given cooling rate. On the other hand, it was also found that organo-montmorillonite reduced the melt-crystallization rate of PBT. It can be concluded that organic ammonium groups in the OM decelerate the crystallization rate of PBT chains possibly due to affecting the chain diffusion through growing crystal face and folding. This study shows that introducing organically modified alumina-silicate layers into the PBT-based composites could significantly reduce the production rate of the injection molded parts during the processing operations. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 77-91, 2012