The lyophilized aqueous crude extract (LACE) from leaves of Persea americana (Lauraceae) species showed a strong inhibitory effect on acyclovir (ACG(r)4 and dlsp TK mutants) and PAA-resistant (PAA(r)5 mutant) herpes simplex virus. After exhaustive washing of LACE using methanol, the soluble fraction was chromatographed on a reverse-phase column giving 11 fractions that were revealed by thin-layer chromatography. Analysis of the antiviral effect of the fractions showed the extract contained compounds that were able to inhibit extracellular virus and the replication of resistant acyclovir HSV. The virucidal effect was concentrated from fraction 4 up to 8. Fraction 7 mainly contains the flavonoid isoquercitrin, and fraction 8 the flavonoid quercitrin. The flavonoid afzelin that is the major substance present in the fraction 9 showed virustatic effect with no virucidal effect. These results show P. americana is a potential plant extract for treatment of herpes simplex virus infections either alone or associated with acyclovir.