Papa Sixtus I (au Xystus) alikuwa Papa kuanzia takriban 117/119 hadi kifo chake takriban 126/128. Alitokea Roma, Italia na jina la baba yake lilikuwa Pastor. Alimfuata Papa Alexander I akafuatwa na Papa Telesphorus. Tangu kale anaheshimiwa kama mtakatifu mfiadini na kutajwa katika Kanuni ya Kirumi. Sikukuu yake ni tarehe 3 Aprili. Watakatifu wa Agano la Kale Orodha ya Watakatifu Wakristo Orodha ya Watakatifu wa Afrika Orodha ya Watakatifu Wafransisko Orodha ya Mapapa Mababu wa Kanisa Maandishi yake katika Patrologia Latina ya Migne https://www.vatican.va/content/vatican/en/holy-father.index.html#holy-father According to the Liberian Catalogue of popes, he served the Church during the reign of Hadrian "from the consulate of Niger and Apronianus until that of Verus III and Ambibulus", that is, from 117 to 126. Eusebius states in his Chronicon that Sixtus I was pope from 114 to 124, while his Historia Ecclesiastica, using a different catalogue of popes, claims his rule from 114 to 128. All authorities agree that he reigned about ten years.