To search for less toxic antiherpetic agents, the inhibitory effects of natural hesperetin on the plaque formation of herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) in Vero cells were examined by the plaque reduction assay in vitro. Hesperetin inhibited plaque formations of HSV-1 and HSV-2 in a dose dependent manner. It also exhibited more potent antiherpetic activity on HSV-2 with selectivity index (SI) of 9.8 than on HSV-1 with SI of 8.4. The combined antiherpetic effects of hesperetin with nucleoside antiherpetic agents, acyclovir and vidarabine, were examined on the multiplication of these two strains of herpesviruses in Vero cells by the combination assay. The results of combination assay were evaluated by the combination index (CI) that was calculated by the multiple drug effect analysis. The combinations of hesperetin with acyclovir on HSV-1 and HSV-2 showed synergistic effects with CI values of $0.29{sim}0.73$ for 50%, 70%, 90% effective levels and those with vidarabine showed partially synergistic or additive effects with CI values of $0.83{sim}1.33$.