Multi-wall carbon nanotubes of medium length (mCNTs) were aggressively tip-ultrasonicated to produce shortened and damaged carbon nanotubes (xCNTs). High-resolution electron microscopic analysis was performed to measure the dimensions of carbon nanotubes (CNTs). Thermo-gravimetric analysis and Raman spectroscopy were used to evaluate the damage in the sonicated CNTs. Short CNTs (sCNTs), in their pristine form (undamaged), were used for comparison with sonicated xCNTs. Good dispersion was achieved when CNTs were bath-ultrasonicated in epoxy resin. The electrical conductivities were measured for cured CNT/epoxy nanocomposites. Compared to shorter CNTs (xCNT and sCNT), mCNT lowered the percolation threshold of CNT/epoxy nanocomposites for electrical conductivity. While ultrasonically shortened xCNTs did give a percolation threshold similar to that of sCNT/epoxy nanocomposites, lower ultimate electrical conductivities were obtained for nanocomposites based on xCNTs due to the presence of structural defects.