A series of novel conjugates of para-carborane with 5-ethynyl-uridine or 2'-deoxyuridine were synthesized. The conjugates were prepared by Sonogashira coupling of para-carborane terminal alkynes and 5-iodo-nucleoside. The designed compounds demonstrated low to moderate cytotoxicity in several cell lines. The antiviral activities of the agents were measured against a panel of DNA and RNA viruses. The most potent compound reported is 5-[(1,12-dicarba-closo-dodecaboran-2-yl)ethyn-1-yl]-2’-deoxyuridine (8), with an IC50 value of 5.5 M and a selectivity index higher than 180. This compound is unusual in that it exhibits antiviral activity against HCMV and is not active against HSV-1, HPIV-3 or EMCV.