Carbon nanotube reinforced copper composites are expected to have superior mechanical and thermal properties. Consolidation of copper-carbon nanotube composite powder is the commonly used technique but uniform distribution of carbon nanotubes in copper matrix remains a challenge. In this study, copper-carbon nanotube composites reinforced with 0.2, 5 and 10 vol.% single walled carbon nanotubes and 5 and 10 vol.% multi-walled carbon nanotubes were processed by high energy milling of pure copper powder with carbon nanotubes. Constituent powders were milled in Attritor mill for 20 h and powder samples were collected after every 5 hour intervals. The composite powders had flake like morphology after prolonged milling. The SEM micrographs of the cross-section of powders revealed layered structure. The particle size distribution showed an increase in the average particle size with increasing milling time for all composite powders except for copper-10 vol.% single wall carbon nanotube. The cold welding and fracturing phenomena of copper-carbon nanotube powders during milling are influenced by the quantity and type of carbon nanotubes. The higher volume fraction of single walled carbon nanotubes has suppressed the cold welding and enhanced the fracturing of copper-carbon nanotube composite powders. © 2013 Elsevier Inc.