The mitochondrial DNA (mtDNA)from liver of Silurzis asotus had been isolated and purified by the method of density gradient centrifugation and DNase I，Rnase digestion. The 8 kinds of restriction endonucleases which were Xho I，Bgl a，EcoR I Pst I，Bgl I，BamH I,Xba I and Hind IQ，had been used to digest the mtDNA. On the S. asotus mtDNA，the digested sites of these enzymes are 0，1，1，1，2，2，7 and 7，respectively. The molecular weight of S. asotus mtDNA is about 10. 84 X 10⁶ and 17.54 kilobase pairs. According to the number and the size of the fragment obtained by digested with single and double enzymes，the restriction enzyme map of mtDNA from S. asotus was constructed.