The arsenic speciation and the content of four toxic arsenic(including As³⁺,As⁵⁺,MMA and DMA)in several main economic shellfishes in our country were analyzed using HPLC-ICP-MS combined with in vitro digestion method.Results showed that S.strictus had the highest total arsenic content(5.68 mg/kg),the second was in S.Subcrenata (4.83 mg/kg),the total arsenic content in C.Farreri, C.Ostreae and H.discus hannai were much lower(2.26-2.70 mg/kg)and three of them had no significant difference.The lowest content was in R.Philippinarum and M.edulis.AsB was the main arsenic speciation in both water extraction and gastrointestinal extraction for all samples,and especially for Scapharca subcrenata,AsB was the only arsenic speciation.About 0.025,0.008 and 0.300 mg/kg As³⁺ were separated in the water extraction of C.farreri, R.philippinarum and S.strictus respectively.In addition,0.115 mg/kg As5+ was also detected in the water extraction of S.strictus.Different concentration of DMA was found in the water extraction of all samples except for S.subcrenata and M.edulis,with the highest content of 0.674 mg/kg in S.strictus.However,except in S.strictus,DMA was detected in the intestinal extraction,none of four toxic arsenic speciations were found in the gastrointestinal extraction of other shellfishes.Present experiments proved that the arsenic speciation in the water extraction which could reflect the real content in shellfishes and in gastrointestinal extraction which could reflect the real content under the gastrointestinal digestion was different,especially for four toxic arsenic speciation.