Electrochemical buffing and chemical polishing can easily control surface roughness on a nano scale. We studied the effect of surface nano roughness on friction in a vacuum and under atmospheric pressure. A vacuum friction measurement system was developed in order to evaluate the sliding friction coefficient under a variable load from 0.49 N to 0.98 mN and at variable pressure from 10(5) to 10(-5) Pa. Friction measurements were executed on type 304 austenitic stainless steels as typical vacuum materials with nano order surface roughness, prepared by chemical polishing and electrochemical buffing. The same value of the friction coefficient was found in a vacuum as under atmospheric pressure when the surface roughness was about 40 nm to 1.5 mum on steel samples. Steel samples with a maximum height of surface roughness (R-max) of around 100 nm shows the same result of low friction in a vacuum as that under atmospheric pressure. (C) 2003 Elsevier B.V. All rights reserved.