Multi-walled carbon nanotubes (MWNTs) were functionalized. with a silane coupling agent. The MWNTs were first coated with inorganic silica by a sol-gel process and then grafted with 3-methacryloxypropyltrimethoxysilane (3-MPTS). The effect of raw MWNTs and silane-functionalized MWNTs on the crystallization behavior of poly(propylene) (PP) was investigated by means of polarized optical microscopy, differential scanning calorimetry, and wide-angle X-ray diffraction. Results obtained from isothermal crystallization experiments indicate that 3-MPTS functionalization affects the crystallization and melting behavior of PP/MWNTs composites remarkably, which can be attributed to the fact that 3-MPTS functionalization of MWNTs leads to a uniform dispersion of MWNTs in PP matrix resulting in the good nucleating effect of MWNTs. (c) 2007 Wiley Periodicals, Inc.