Double‐walled carbon nanotube (DWCNT)‐reinforced polyester nanocomposites were prepared and tested to characterize their mechanical properties. The DWCNTs were functionalized to improve their dispersion within the polyester matrix. The improvement in the mechanical properties shows that the functionalized DWCNTs have better distribution within, and good adhesion with, the polyester matrix. A comparison of the mechanical properties of nanocomposites reinforced by functionalized and nonfunctionalized DWCNTs confirms that the functionalization leads to substantially improved composites. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers