PURPOSE: To impart excellent vibration-damping quality and strength character istics over a wide temperature range to a plastic product for an automobile, by incorporating a composition comprising a tackifier resin and a specified polyolefin resin into a polyamide resin.

CONSTITUTION: A composition (a) obtained by mixing 20W80wt% tackifier resin and 80W20wt% polyolefin resin compatible with the tackifier resin and a polyamide resin, and a polyamide resin (b) are mixed preferably in the ratio of a to b of 10W50:90W50(wt%). The examples of tackifier resins include a cumarone resin, a terpene phenol resin, and a hydrogenated rosin resin; prefer ably the second or the third resin is used. As a polyolefin resin having the above-mentioned characteristics, a polymer or a copolymer which consists of one or more α-olefin monomers such as ethylene and propylene, and contains one or more functional groups such as carboxyl and epoxy groups in the molecu lar chain (e.g., a polyethylene modified with maleic anhydride) is preferably used.