This invention relates to an aromatic oligomer represented by the following formula (1): (A—F)n—A   (1) wherein A is a unit comprising (a) 30-90 wt % of a bicyclic or tricyclic aromatic compound and (b) 10-70 wt % of a phenol, F is methylene or a mixture of methylene and —CH2OCH2— and n is a number of 1-100. The aromatic oligomer is obtained by and reaction of a polycyclic aromatic compound such as naphthalene and benzothiophene, a phenol and formaldehyde compound in the presence of an acid catalyst. The aromatic oligomer is odorless and useful for various applications. In particular, when incorporated in rubber or resin, the aromatic oligomer can perform execellently as a tackifier in a wide temperature range or perform excellently as a vibration damping agent.