Abstract: Airborne particles were collected from urban areas of Beijing and Tianjin using an FA-3 aerosol cascade sampler in summer 2002. Organochlorine pesticides residues in various size fractions of the samples were measured.δ-HCH,p,p′-DDD and p,p′-DDT were all detectable.Concentrations of HCHs(α-HCH+β-HCH+γ-HCH+δ-HCH)were 0.240 ng/m 3 and 0.581 ng/m 3,and DDTs(p,p′-DDT,p,p′-DDD+p,p′-DDE) were 0.962 ng/m 3 and 1.874 ng/m 3 in the samples from Beijing and Tianjin,respectively.The levels of organochlorine pesticide residues in the sample from Tianjin were much higher than those from Beijing.The size distributions of HCHs in both samples and DDTs in the sample from Beijing were unimodal,while the size distribution of DDTs in the sample from Tianjin was trimodal.The median diameter and dispersion degree of HCHs and DDTs were at 2.1～2.5 μm and 3.1～3.7 μm respectively.