Thermal properties and nonisothermal crystallization kinetics of polyolefin nanocomposites (high-density polyethylene/multiwalled carbon nanotubes) were characterized by differential scanning calorimetry and thermogravimetric analysis In situ metallocence polymerization was used to prepare nanocomposites of multiwalled carbon nanotubes (MWCNTs) and high-density polyethylene (HDPE) This polymerization method consists of attaching a metallocene catalyst complex onto the surface of the MWCNTs followed by surface initiated polymerization to generate polymer brushes on the surface A kinetic equation for the nonisothermal crystallization was employed to analyze the crystallization characteristics of the nanocomposites The Avramic exponent, n, can be reasonably well determined from the nonisothermal crystallization exotherm The polarized optical microscopy showed that neat polyethylene possessed a well-developed spherulite morphology, whereas the nanocomposites displayed elongated entities that subsequently developed as bundlelike entities Nonisothermal analysis implicitly provides clues about the morphological development history and HDPE molecular ordering around the carbon nanotubes