To newly develop a resin tackifier having a good color tone, easy polymerized and having excellent adhesive properties such as adhesion, cohesion power and tackifying ability.

This tackifier resin is obtained by polymerizing (A) 8-10C aromatic unsaturated hydrocarbons and (B) rosin esters prepared by esterifying at least one kind of rosins and rosin derivative with alcohols or further with (C) cyclic diolefins such as ethylidene norbornene, dipentene and dicyclopentadiene having no polar group. The resin exhibits excellent adhesive properties with a good balance among the cohesion power, the tackifying ability and retentivity by polymerizing the (A) and (B) or further (C), for example, compared with a resin in which the (A) and (B) are simply mixed. Adhesive properties to an polyolefin are improved by additionally polymerizing the (C).