Cup-stacked carbon nanotube (CSCNT) is considered to be a superior candidate as a polymer modifier. CSCNTs are susceptible to reduction in length during the dispersion process because of their specific structure. As it is well-known that CNT length or aspect ratio has great impact on physical properties (e.g. mechanical, thermal, electrical properties) of nanocomposites, the effect of mixing process on the length distribution of CSCNTs is investigated in the present study. Length distribution of CSCNTs with and without length control is measured using SEM, and expressed as a log-normal distribution. Effects of length distribution on the mechanical properties of CSCNT-dispersed composites are estimated using a micromechanical model for multiphase inclusions. Copyright © 2008 by JSCM.