Poly(trimethylene terepthalate) (PTT) has in recent years, attracted much interest for its application in fibers and engineering thermoplastics, due to its outstanding properties such as good resilience and elastic recovery [1, 2]. As a typical semicrystalline polymer, the crystallization behavior of PTT is the primary property that affects its physical properties and processing conditions, and thus many articles have appeared describing this topic [3–10]. In previous works, we reported the crystallization kinetics of PTT including the secondary crystallization process, and the crystallization behavior of PTT at high undercoolings was also explored [6, 7]. A series of copolyesters based on PTT with modified thermal properties have been prepared and their composition dependence of thermal properties was also presented [8–10]. Moreover, recently increasing attention has been given to the fabrication and the property studies of polymer/carbon nanotubes (CNTs) composites due to the high aspect ratio, nanosize in diameter, very low density, excellent physical properties of CNTs, and the remarkably enhanced physical properties of the composites [11–15]. However, so far there is a little research on the crystallization behavior of such polymer nanocomposites, especially in the nucleation effect of CNTs on the polymer matrix despite of its potential, academic, and technological values. In this communication, PTT composites with multiwalled carbon nanotubes (MWNTs), in which the nanotube consists of several layers of coaxial carbon tubes [16, 17], were prepared, and the influence of MWNT on crystallization of PTT matrix was discussed. To our knowledge, it is the first time that poly(trimethylene terephthalate)/multiwalled carbon nanotube composites were prepared and their crystallization behavior was presented. PTT ([g] = 0.0795 m/kg at 298 K) used in this study is the same polymer which has been described in one of our previous articles [6]. MWNTs were purchased from Bill Nanotech Co., Ltd (Shenzhen, China). These MWNTs were produced via the chemical vapor deposition (CVD) method and have lengths up to a few microns and diameters between 70 and 100 nm. The purchased MWNTs were purified to remove amorphous carbon and iron impurities [18]. In a typical experiment, an MWNT sample was heated and refluxed in an aqueous HNO3 solution (2.6 M) for 13 h. After filtering through a Teflon-PTFE membrane, the remaining solid was washed with deionized water until the pH was neutral. The purified MWNTs were then functionalized by tetrabutyl titanate to enhance the compatibility of MWNT with PTT. To fabricate PTT–MWNT composites, weighed PTT sample was dissolved in the solution of 1:1 (w/w) 1,1,2,2-tetrachloroethane/phenol at 353 K to form a clear solution. Appropriate amount of functionalized MWNT was weighed according to the required percentage, and was added to the solution. The mixture was refluxed with stir for 4 h to form a homogeneous suspension and then sonicated for 1 h. Finally, the mixture was cast into an aluminum mold in the form of a film. The mold with the suspension was vacuum dried in an oven at 373 K for 48 h. The resultant composite was denoted according to the weight percentage of MWNT in Y. Xu (&) H.-B. Jia J.-N. Piao Department of Polymer Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094, P.R. China e-mail: xuyong@zuaa.zju.edu.cn