Although many studies have been conducted in the past few years on the possibility of using carbon nanotube (CNT) to improve the performance of polymer-based materials, some of the results were contradictory and lack of coherence. Thus, the in-depth understanding of CNT composites is required. In this paper, single-walled carbon nanotubes (SWNTs), which were functionalized by sonicating with nitric and sulfuric acids, will be used to fabricate a SWNT/epoxy composite. There are two reasons for functionalizing the SWNTs, they are (i) to improve the dispersion of the SWNTs in polymer, and (ii) to improve the interfacial bonding properties between the SWNTs and polymer matrix. Tensile property test and micro-hardness test will be carried out to examine the mechanical properties of the composites with different SWNT contents. Thermogravimetry Analysis (TGA) will be used to evaluate the thermal properties of the composites. Scanning Electron Microscope (SEM) will also be used to investigate the failure mechanism of the composites after tensile test. A comparison of the composites with functionalized and non-functionalized SWNTs will be given to elaborate the effect of nanotube functionalization.