Cosimo Fancelli (c.1620 – 3 April 1688) was an Italian sculptor of the Baroque period, active mainly in Rome. He was the son of the artist Carlo Fancelli from Arezzo. Like his brother, the sculptor Giacomo Antonio Fancelli, he began his career as an assistant in the studio of Bernini. He is said to have helped sculpt the figure of the Nile in the Fountain of the Four Rivers at Piazza Navona, though this is also attributed to his brother Giacomo.
He then allied with Pietro da Cortona, and helped with the decoration at Santi Luca e Martina (c. 1649), Santa Maria della Pace (1656), Santa Maria in Via Lata (c. 1660), San Carlo al Corso (after 1665), and the vault of the Chiesa Nuova (1662–65). Among the pupils of Cosimo was Francesco Cavallini. In 1669, Bernini assigned him to complete the Angel with Sudarium on Ponte Sant'Angelo.