Carbon nanotubes (CNTs) deposited by chemical vapor deposition (CVD) were treated by ball milling. The morphologies and field emission properties of the treated CNTs depending on milling time were studied. The emission turn-on field is increased, and the field emission current density is reduced, when the milling time increased from 0.5 to 3 h. The as-deposited long CNTs were cut to short CNTs (similar to 1 h) and micro-particles (> 1 h) with increasing of the milling time. It is found that the optimized milling time is 0.5-1 h, the treated CNTs showed excellent field emission properties, such as low turn-on field, high emission current density and uniform luminescence spots distribution. (c) 2006 Elsevier B.V. All rights reserved.