Diglycidyl ether of bisphenol A (DGEBA)-bridged polyorganosiloxane precursors have been prepared successfully by reacting diglycidyl. ether of bisphenol A epoxy resin with 3-aminopropyltriethoxysilane. Acid-modified and unmodified multiwalled carbon nanotube (MWCNT) were dispersed in the diglycidyl ether of bisphenol A-bridged polyorganosiloxane precursors and cured to prepare the carbon nanotube/diglycidyl ether of bisphenol A-bridged polysilsesquioxane (MWCNT/DGEBA-PSSQ) composites. The molecular motion of MWCNT/DGEBA-PSSQ nanocomposites was studied by high-resolution solid-state C-13 NMR. Acid-modification can improve the affinity between MWCNT and the polymer matrix. The molecular motion of the DGEBA-PSSQ decreased with acid-modified MWCNT content. However, when unmodified MWCNT was used, the molecular motion of the DGEBA-PSSQ was increased. SEM and TEM microphotographs confirm that acid-modified MWCNT exhibits better dispersion than unmodified MWCNT in DGBEA-PSSQ. The dynamic mechanical properties of acid-modified MWCNT/DGBEA-PSSQ composites are more favorable than those of unmodified MWCNT. T-g of the DGEBA-PSSQ decreased from 174.0 degrees C (neat DGEBA-PSSQ) to 159.0 degrees C (1 wt % unmodified MWCNT) and 156.0 degrees C (1 wt % acid-modified MWCNT). The storage modulus (at 30 degrees C) of the DGEBA-PSSQ increased from 1.23 x 10(9) Pa (neat DGEBA-PSSQ) to 1.65 x 10(9) Pa (1 wt % acid-modified MWCNT). However, when unmodified MWCNT was used, the storage modulus of the DGEBA-PSSQ decreased to 6.88 x 10(8) Pa (1 wt % unmodified MWCNT). At high temperature, above 150 degrees C, storage modulus of nanocomposites was higher than that of neat polymer system. (C) 2008 Wiley Periodicals, Inc.