A process for producing a hydroxystilbene derivative represented by formula (1) (wherein X1-X4 independently represent a hydrogen atom, a hydroxy group, a saturated or unsaturated linear or branched alkoxy group having 1-10 carbon atoms, or a saturated or unsaturated linear or branched alkyl group having 1-10 carbon atoms; Z1 and Z2 independently represent a hydrogen atom, or a group represented by the formula (2) (wherein X5 and X6 independently represent a hydrogen atom, a hydroxy group, a saturated or unsaturated linear or branched alkoxy group having 1-10 carbon atoms, or a saturated or unsaturated linear or branched alkyl group having 1-10 carbon atoms); and Z1 and Z2 may be the same as or different from each other; wherein X1-X6 may be the same as or different from one another), which is characterized by heating a 4-hydroxycinnamic acid compound and a hydroxystilbene compound in the presence of a metal salt.