In this research, multiwalled carbon nanotube (MWNT) was oxidized and then modified to form carboxylic groups ( COOH) on the surface and the end of the tube. After that, the MWNT was added to polyimide matrix to enhance its mechanical and electrical properties by in situ polymerization and blending. The PI/MWNT composites were obtained by spin coating and multistep thermal curing process. The comparison of in situ polymerization and blending as well as the effect of unmodified and modified MWNT were discussed in this study. The results indicate that in situ polymerization is able to make a perfect dispersion by adding modified MWNT into polyimide matrix. Thermal and mechanical properties of the composites can be improved by hydrogen bonding interaction between the modified MWNT and polyimide matrix. Electrical resistance of the composites can be decreased to meet the criterion of electrostatic charge (ESC) mitigation as the surface resistance is reduced into the range of 10(6)-10(10) Omega/cm(2) by adding modified MWNT. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 3111-3117, 2010