On the basis of the potent antiviral activity of acyclovir and ganciclovir, selenoacyclovir (2a) and selenoganciclovir (2b) were designed based on bioisoteric rationale and synthesized via the diselenide 7 as the key intermediate. Compound 2a exhibited potent anti-HSV-1 and -2 activities while 2b exerted moderate anti-HCMV activity, indicating that these nucleosides can serve as a novel template for the development of new antiviral agents.