The present invention aims to provide an anti-norovirus agent that has high norovirus-inactivating activity and is safe for the human body, and an anti-norovirus composition that contains the anti-norovirus agent and is useful for disinfection and infection control against the norovirus. An anti-norovirus agent according to the present invention is characterized by containing, as an active ingredient, an extract from a plant of the genus Diospyros containing tannin (hereinafter referred to as a "persimmon extract"), preferably a persimmon extract produced by heating squeezed juice or an extract from the fruit of a plant of the genus Diospyros or treating the squeezed juice or the extract with an alcohol. An anti-norovirus composition according to the present invention is characterized by containing the anti-norovirus agent and at least one selected from the group consisting of alcohols, surfactants, bactericides, humectants, and cosmetic fats and oils, and preferably further containing an organic acid, such as citric acid, and/or a salt thereof or vitamin C.