About 0.001 to 5 parts by weight of a hindered phenol-series compound, about 0.01 to 5 parts by weight of a weather (light)-resistant stabilizer, and about 0.001 to 10 parts by weight of a spiro-compound having a triazine ring are added to 100 parts by weight of a polyacetal resin. The spiro-compound may be a compound represented by the following formula (1). The polyacetal resin composition may further comprise a coloring agent, a processing stabilizer, a heat stabilizer, and others. ##STR1## wherein R.sup.1 and R.sup.2 are the same or different, each representing an alkylene group, an arylene group, or an aralkylene group.