A stabilized polyolefin composition having improved weathering resistance is provided, whereby the following four components are incorporated into a polyolefin:(A) a hindered piperidine compound having a molecular weight of more than 750, such as poly-{[6-morpholino-1,3,5-triazine-2,4-diyl][2,2,6,6-tetramethyl-4-piperidyl)imino]hexamethylene[2,2,6,6-tetramethyl-4-piperidyl)imino]},(B) a hindered piperidine compound having a molecular weight of less than 500, such as bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate,(C) a benzoate compound such as 2,4-di-t-butylphenyl 3,5-di-t-butyl-4-hydroxybenzoate, and(D) a phosphorus-containing compound such as bis(2,4-di-t-butylphenyl) pentaerythritol diphosphite.