Multi-walled carbon nanotubes (MWCNTs) were modified with an H2SO4/HNO, acid treatment, and subsequently functionalized with a (3-glycidyloxyporpl)trimethoxysilane coupling agent. The functionalized MWCNTs showed considerably improved dispersion in H2O and N-Methyl-2-pyrrolidinone (NMP), and the MWCNT suspension exhibited long-term stability. The functionalized MWCNTs were characterized with Raman spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, and scanning electron microscopy (SEM) with an attached energy dispersive X-ray analyzer. Polyimide (PI)/MWCNT nanocomposites were synthesized from 4,4'-oxydianiline (ODA) and 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) using NMP as solvent. Improved MWCNT dispersion and enhanced interfacial adhesion were observed on the tensile fracture surfaces of the polyimide nanocomposite with functionalized MWCNTs.