Abstract: A medicinal plant-derived antiviral powder is provided as obtained by collecting a medicinal plant having an antiviral action, immediately quickly heating the plant to de-activate enzymatic activity, subjecting to low temperature drying, and milling after the quick heating or low temperature. The powder may be extracted with hot water or a lower alcohol to obtain antiviral extract. These powder and extract may be utilized as preparations, particularly, a powder, comprising an effective amount thereof The powder and extract obtained by treating, as a medicinal plant, young leaves of Rhus verniciflua and a flower portion of Ulmus davidiana var.japonica are useful.