Abstract: The changes of diamondoid compounds in the fuel oil sample during natural long-term weathering (0~100 days) were presented.Adamantanes in fuel oil were not found after 60 day natural weathering,adamantanes in crude oil from Bohai sea No.1 were not found after 45 day natural weathering.The concentrations of diamantanes slightly decrease with an increase of weathering time and diamantanes have stronger weathering-resistant capabilities.According to the "Student's t" test,seven ratios of diamantanes had no apparent changes which could indicate the source of the samples during 20 days weathering.Diamantanes ratios of DMDI-3,DMDI-4 and DMDI-5 are essentially unaltered after 100 days natural weathering which could indicate the source of the samples during natural long-term weathering.The diagnostic ratios of diamantanes in fuel oil are relatively more stable compare with those in crude oil.