Abstract: The gene expression patterns of P4501A1, P-gp and HSP70 of Portunus trituberculatus were both measured using realtime fluorescence quantitative PCR during crab exposed to environmentally relevant concentration of Benzoapyrene (0.05, 0.15, 0.45 g/L, respectively) and the release of the test.The results showed that P451A1, P-gp and HSP70 mRNA could be induced, besides, the content of P4501A1 mRNA induced is more significantly(P0.05).The content of three genes mRNA were decrease markedly after the release of the test and the P4501A mRNA has more obvious changes.In a word, The gene expression of P4501A1, P-gp and HSP70 were increase at the beginning of Benzoapyrene exposure, and then decreased after the release of the test.The above data suggest that Benzoapyrene could induced high concentration of P451A1 mRNA in the liver of crab to monitor indicates contamination of organic pollutants in the water of PAHs.