Abstract: There is a serious need for compounds that are effective in the treatment of cancer and virus (HIV. Human Immunodeficiency Virus,etc.). Among the large number of nucleoside analogs which have been synthesized and evaluated^(1-2) recently several 5'-alkylthio nucleosides have been reported to exhibit good antitumor and antiviral activities^(3-4). Their anticancer mechanism involves blocking cancer cell proliferation and inhibiting the cytoplasmic isozyme(C-TK)⁽⁵⁾, one isozyme of thymine kinase, which predominates in human tumor cell lines⁽⁶⁾. As we know, many acylic nucleoside analogs have appeared good biological activities⁽⁷⁾. It is reported that they can also act on some thymine kinases and end up the propagation of the viral DNA chain⁽⁸⁾.