Thirty ellagitannins originated from some Euphorbiaceous plants were tested for the inhibitory activities against AMV reverse transcriptase and replication of HIV-1 using syncytia forming assay. Most of ellagitannins showed strong inhibitory activities against AMV reverse transcriptase. Some ellagitannins including geraniin, mallotusinin, elaeocarpusin, euphorscopin and jolkianin, showed significant inhibitory activities of syncytia formation of supT1 cell line.