The roadside dusts collected from three selected sites with marked differences in annual average daily traffic (AADT) values were divided into size classes according to particle size. The total, extractable, and water-soluble metal contents were determined using mixed acid, 1 M NH4OAc (pH 7.0), and distilled water as extractants. It was found that dust particles with a size smaller than 125 microns belonged to a homogeneous group and did not have a significant difference in metal contents. In using dust as a parameter to indicate the level of Pb contamination, a particle size of 125 microns and the extractable metal contents, using NH4OAc, should be used.