Single-walled carbon nanotubes (SWNTs) are functionalized through both covalent and noncovalent bonding approaches to enhance dispersion and interfacial bonding. The coefficient of thermal expansion (CTE) of the functionalized-SWNT-reinforced epoxy composites are measured with a thermal mechanical analyzer (TMA). Experimental results indicate that changes of the glass-transition temperature (Tg) in functionalized SWNT–polymer composites are dependent upon the functionalization methods. The CTE below the glass-transition temperature of nanocomposites with a 1 wt % loading of nanotubes is substantially diminished compared to a neat polymer. A reduction in the CTE of up to 52 % is observed for nanocomposites using functionalized nanotubes. However, the CTE above the Tg significantly increases because of the contribution from phonon mode and Brownian motions of a large number of SWNTs in resin-crosslinked networks, but the increments are compromised by possible interfacial confinement. A tunable CTE induced through nanotube functionalization has application potentials for high-performance composites, intelligent materials, and circuit protections.