Disclosed is an anti-plant-virus agent that has a preventative and therapeutic effect on plant viral diseases. The anti-plant-virus agent is characterized by containing at least one compound selected from the group consisting of an ascorbic acid derivative represented by formula 1 (wherein R-R each independently represent a hydrogen atom, -SOH, -POH, a glycosyl group, or -COR； R represents an unsubstituted or substituted C1-30 alkyl group, or an unsubstituted or substituted C2-30 alkenyl group； and R-R may not all be hydrogen atoms at the same time), and a salt thererof.
