The invention provides a glycoluril represented by the general formula (Z): wherein the group Z represents a carboxyalkyl, a glycidyl or an allyl group; R1 and R2 each independently represents a hydrogen atom, a lower alkyl or a phenyl group; R3 , R4 and R5 each independently represents a hydrogen atom or the group identical with the group Z; however, when the group Z is a carboxyalkyl group, R3 ,R4 and R5 are the same carboxyalkyl groups as the group Z; and when the group Z is an allyl group, R 5 represents a hydrogen atom. The invention further provides various resin compositions, for example, polyester resin compositions, epoxy resin compositions, and silicone resin compositions each comprising the glycoluril.