Traditional herbal medicines have been safely used for the treatment of various human diseases since ancient China. We selected 10 herbal extracts with therapeutic antiherpes simplex virus type 1 (HSV-1) activity. Among these, Geum japonicum Thunb., Rhus javanica L., Syzygium aromaticum (L.) Merr. et Perry, or Terminalia chebula Retzus showed a stronger anti-HSV-1 activity in combination with acyclovir than the other herbal extracts in vitro. When acyclovir and/or a herbal extract were orally administered at doses corresponding to human use, each of the 4 combinations significantly limited the development of skin lesions and /or prolonged the mean survival times of infected mice compared with both acyclovir and the herbal extract alone (P<0.01 or 0.05). These combinations were not toxic to mice. They reduced virus yields in the brain and skin more strongly than acyclovir alone and exhibited stronger anti-HSV-1 activity in the brain than in the skin, in contrast to acyclovir treatment by itself. Combinations of acyclovir with historically used herbal medicines showed strong combined therapeutic anti-HSV-1 activity in mice, especially reduction of virus yield in the brain