The present study is focused on the surface roughness of abrasive waterjet (AWJ) cut surfaces. This study explains the effects of feed rate and thickness of workpiece on the roughness. Considering experimental data, effects of the composition of the material on surface roughness are assessed. The study also evaluates the deformation effect of AWJ on workpieces that have the same composition but different thickness. In the study pure aluminium, Al-6061 aluminium alloy, brass-353 (alpha + beta brass), AIST 1030 and AISI 304 steel materials are cut with AWJ at different feed rates. Improvement in surface roughness of pure aluminium remains in narrow limited range when compared with the ratio of decrease in feed rate. Experimental results explain "cutting wear" and "deformation wear" mechanisms are effective in cutting both of the mild and the brittle structure materials with AWJ. The pressure of the AWJ negatively affects the surface roughness as the thickness of the material decreases. Brass and AISI 1030 materials that have higher strength than aluminium result in higher surface roughness for thinner workpieces. Reducing feed rate from 25 to 20 mm/min deteriorated the Surface properties of 20 mm thickness workpiece of AISI 304, in contrast to all of the other studied 20 mm thickness materials. Additional Studies are required to understand this different behaviour of 20 nun thickness specimen of AISI 304. (C) 2004 Elsevier B.V. All rights reserved.