Several types of virus were found to have a strong association with different types of cancers. Thus, a selective antiviral compound without toxicity upon long-term usage will be useful not only for the treatment of viral diseases but also for the prevention or the delayed onset of those cancers, which have a strong association with viruses. L(-)Nucleoside analogs were discovered recently in my laboratory as an important class of antiviral and anticancer chemical entities. L(-)SddC (3TC, Lamivudine), FTC, Fd4C, and L(-)FMAU are potent anti-HBV compounds with different pharmacological profiles. These compounds may be useful in the prevention or delayed onset of hepatocellular carcinoma associated with HBV. L(-)I-OddU is the most potent anti-Epstein-Barr Virus (EBV) compound without cytotoxicity and animal toxicity upon long-term dosing which gives the pharmacological levels of the drug in plasma. This compound may have the potential to prevent B-cell lymphoma associated with patients undergoing organ transplants in addition to its potential use for the treatment of EBV infection.