Soil samples collected from an ancient paddy soil profile(BP 6 000 a)were analyzed with HPLC for 15 polycyclic aromatic hydrocarbons(PAHs)in order to determine their contents and distribution patterns.The total PAHs in various soil layers varied between 25.9 and 202.9μg kg^-1,with the highest observed in the surface horizon.Nap,Phe,Fla and Pyr were the four major compounds in a decreasing order of Nap>Phe>Fla>Pyr in terms of abundance.PAHs of 4 or more rings accounted for 51.8% of the total.In deeper layers,total PAHs decreased sharply,and the number of detectable compounds also decreased.Moreover,2-and 3-ring PAHs became the dominant compounds in these layers,but 4-or more-ring PAHs still formed a large portion of the PAHs in the ancient paddy soil.The results of the principal component analysis and cluster analysis indicated that Chr,BkF,BaA,IcP,BbF,Pyr,BaP,DaA and Fla were products of human activities,Flu and Phe were formed in biological process under reducing conditions,while Nap,BgP and Ant might result from the joint effect of human activities and biological process.