Lanzhou is situated in semi-arid regions of Northwest china,airborne particles has a major impact on the air quality of that,especially dust storms occur.This paper describes the TSP mass concentration and its water-soluble ions composition in the ambient air of Lanzhou.The samp site was chosen on the roof of a seventh story building (about 50 m above the ground level) in lanzhou university,located in urban area of Lanzhou,the particle samples were collected from November 2004 to November 2005,four in a week.By analysising,it was found that the annual average value of the mass concentration was 0.44 mg/m 3 and went beyond the national standard(III) badly.