A polyacetal resin composition. An aliphatic polycarboxylic acid having four or more carbons and two or more carboxyl groups and a hindered-phenol antioxidant are incorporated into a polyacetal copolymer obtained by copolymerizing trioxane as a major monomer with a cyclic ether and/or cyclic formal each having at least one carbon-carbon bond as a comonomer using a specific heteropoly acid as a polymerization catalyst, adding, to the resultant reaction product, a compound which is any of the carbonates, hydrogen carbonates, and carboxylates of alkali metal elements or alkaline-earth metal elements, the hydrates of these, and the hydroxides of alkali metal elements or alkaline-earth metal elements, and melt-kneading the mixture to deactivate the polymerization catalyst.