St. Michael of Lillo (Spanish: San Miguel de Lillo, Asturian: Samiguel de Lliño) is a Roman Catholic church built on the Naranco mount, near the Church of Santa María del Naranco in Asturias. It was consecrated by Ramiro I and his wife Paterna in the year 848. It was originally dedicated to St. Mary until this worship passed to the nearby palace in the 12th century, leaving this church dedicated to Saint Michael. It is a UNESCO World Heritage Site since 1985.
It originally had a basilica ground plan, three aisles with a barrel vault, although part of the original structure has disappeared as the building collapsed during the 12th or 13th century. Nowadays, it conserves its western half from that period, together with several elements in the rest of the church such as the fantastic jambs in the vestibule or the extraordinary lattice on the window of the southern wall, sculpted from one single piece of stone.