PURPOSE: To provide the titled compsn. having improved properties with regard to discoloration resistance and heat decomposition within cylinders of molding machines, by blending a polyacetal resin with an ionomer and an org. nitrogen- contg. compd.

CONSTITUTION: Part of the carboxyl groups of an olefin copolymer obtd. by copolymerizing an olefin such as ethylene, propylene, etc., with a carboxylic acid such as (meth)acrylic acid, maleic acid, etc., are subjected to an intermolecular crosslinking reaction with a mono- to trivalent metal ion such as Ca2+, Zn2+, Mg2+ to obtain an ionomer (B). 100pts.wt. polyacetal resin (A) is blended with 0.01W25pts.wt. component B and optionally, not less than 100pts. wt. org. nitrogen-contg. compd. (C) (e.g., melamine), an antioxidant, a light stabilizer, a lubricant, a nucleating agent, a parting agent, etc. (D).