In plants, viral diseases are second only to fungal diseases in terms of occurrence, causing substantial damage to agricultural crops. The aqueous extract of Alpinia zerumbet exhibits inhibitory effect against virus infection in Solanaceae members. In this study, we isolated an anti-plant-virus molecule from the extract using a conventional method of a combination of reversed phase column chromatography, dialysis, and lyophilization. The anti-plant-virus molecule was identified as proanthocyanidin, which mostly consisted of epicatechin and showed more than 40 degrees of polymerization.