A polyoxymethylene copolymer prepared by copolymerizing a mixture comprising trioxane and 1,3-dioxolane in the presence of at least one polymerization catalyst selected from the group consisting of boron trifluoride, a boron trifluoride hydrate and a coordination complex compound of an organic compound containing an oxygen atom or a sulfur atom with boron trifluoride, wherein the 1,3-dioxolane has a 2-methyl-1,3-dioxolane content of not more than 500 ppm by weight and a 1,3-dioxolane peroxide content of not more than 15 ppm by weight in terms of hydrogen peroxide, and contains at least one hindered phenol in an amount of from 10 to 500 ppm by weight, each based on the weight of the 1,3-dioxolane.