Catechism of the Catholic Church §328 — excerpt
The existence of the spiritual, non-corporeal beings that Sacred Scripture usually calls "angels" is a truth of faith. the witness of Scripture is as clear as the unanimity of Tradition.
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.