To provide a resin composition of polyacetal copolymer having practically satisfactory heat resistance, mechanical properties and moldability, further excellent in wet heat resistance; and a molding thereof.

This polyacetal resin composition includes, based on a polyacetal copolymer (A) in which the content of oxyalkylene unit per 100 moles of oxymethylene units is 0.4-17.0 moles: 0.01-1.0 pt.wt. of an amine-substituted triazine compound (B); 0.01-5.0 pts.wt. of a hindered phenol (C); 0.001-3.0 pts.wt. of a hindered amine (D); and 0.005-0.05 pt.wt. of one or more metal-containing compounds (E) selected from a group consisting of a hydroxide, inorganic acid salt or alkoxide of alkali metals or alkaline earth metals.