A weather-resistant thermoplastic resin composition excellent in processing stability is provided which comprises 100 parts by weight of a mixture of 40-100 parts by weight of a vinyl chloride polymer and 0-60 parts by weight of a polymer containing no chlorine and having a glass transition temperature of 100.degree.-200.degree. C.; 4-25 parts by weight of an impact strength modifier containing no double bond; and 0.1-1.0 part by weight of a hindered amine light stabilizer. Molded articles made from this composition are especially excellent in weather resistance and are useful as pipes outdoors or building materials.