Abstract: Objective To study the level of exposure to polycyclic aromatic hydrocarbons(PAHs)and its population distribution and seasonal variation among pregnant women in urban Beijing.Methods Totally 205 pregnant women were recruited in Haidian Maternal and Child Health Hospital in Beijing from March 2013 to June 2014.Elbow venous blood samples of the women were collected and plasma samples were obtained with centrifugalization.After liquid-liquid extraction,cleanup and concentration,the concentrations of 15 PAHs in the plasma samples were measured with gas chromatography-mass spectrometer(GC-MS).Results The detection rates of low-molecular-weight PAHs(L-PAHs)in the plasma samples were between 75.1% and 97.6%,while those of high-molecular-weight PAHs(H-PAHs),including benzo(a)pyrene(BaP),indeno(1,2,3-cd)pyrene(IcdP),dibenzo(a,h)anthracene(DahA)and benzo(g,h,i)perylene(BghiP),were all less than 5% and the other H-PAHs,including pyrene(Pyr),benzo(a)anthracene(BaA),chrysene(Chr),benzo(b)fluoranthene(BbF) and benzo(k) fluoranthene(BkF),were between 53.7% and 100%.The median and interquartile range(IQR)of ΣPAHs(the sum of 15 PAHs) was 1484.52,563.23-2401.09 ng/g;the concentration of phenanthrene(Phe) was the highest(793.33,174.11-1515.69 ng/g),while that of acenaphthylene(Acy)was the lowest(29.04,14.84-43.81 ng/g) among all L-PAHs;and Chr was the highest(45.94,13.51-65.42 ng/g)among all H-PAHs.There were no significant differences in the concentrations among the women of various age,pre-pregnancy body mass index(BMI),education,and passive smoking status for all PAHs.The plasma concentrations of anthracene(Ant),fluoranthene(Flua),Pyr,BaA,Chr,BbF,BkF,and ΣH-PAHs(the sum of 9 H-PAHs) were significantly different for the blood samples collected during different seasons.The plasma concentrations of PAHs showed a down trend as seasonal variation,with the sequence of autumn,summer,winter,and spring for Ant;spring,autumn,summer,and winter for Flua;winter,autumn,summer,and spring for Chr,BbF and ΣH-PAHs;autumn,winter,summer,and spring for Pyr;and winter,autumn,spring,and summer for BaA,respectively.Conclusion The level of exposure to PAHs among pregnant women in urban Beijing is at a relatively high level as a whole,and presents no significant disparity between groups.But the level of exposure to PAHs shows some seasonal variations which may be related to changes in dietary intake,inhalation intake and personal behaviors of the women.