This invention relates to a resin composition useful as a vibration-damping agent and the like. The resin composition is formulated by adding 1 wt % or more of styrenated phenol obtained by the reaction of a phenol with styrene to a polycyclic aromatic oligomer obtained by condensing a polycyclic aromatic compound containing 2 to 3 rings and formaldehyde. The polycyclic aromatic oligomer is obtained by the reaction of a polycyclic aromatic compound with formaldehyde and, if necessary, further with a phenol in the presence of an acid catalyst and has a number average molecular weight of 300 1000. The styrenated phenol is obtained by the reaction of 1 mole of a phenol with 1 2.5 moles of styrene in the presence of an acid catalyst.