Pier Francesco Tosi (around 1653 - 1732) was a castrato singer and writer on music.

He was born in Cesena and became one of the most famous castrati of his day. He performed throughout Europe and taught singing in London. He is best known as the author of Opinioni de' cantori antichi e moderni (1723), a treatise on singing. This was translated into English as Observations on the Florid Song by J. E. Galliard in 1742 and into German as Anleitung zur Singkunst by Johann Friedrich Agricola (who also provided an extensive commentary of his own) in 1757. Tosi also write some vocal works. He died in Faenza.

Pier Francesco Tosi was the son of Giuseppe Felice Tosi, a composer and organist.