Abstract: The concentration and composition characteristics of n-alkanes in seawater and sediment of Xiamen bay were detected to elucidate their sources and the condition of petroleum pollution.The concentration of oil in seawater conformed to the first class of seawater quality standards.The concentrations of n-alkanes were higher than those in 1995 indicating the increased risk of petroleum pollution in seawater.The concentrations of n-alkanes in sediments were ranged from 1.80 μg/g to 4.27 μg/g.The characteristic parameters of Pr/Ph,L/H,CPI dominant peaks and so on suggested the sediments in Xiamen bay were reducible.Furthermore,the n-alkanes in Tong'an bay,western Xiamen and Jiulong estuary were double perk-clustered,mainly from terrestrial sources and the sediments in these areas might be contaminated by petroleum while that in eastern Xiamen and Dadeng were one perk-clustered,mainly from marine organisms but could not exclude the possibility of petroleum pollution.