Attilio Malachia Ariosti (or Frate Ottavio) (5 November 1666 – 1729) was a Servite Friar and Italian composer in the Baroque style.

He became a monk in 1688 at age 22, but he soon obtained permission to leave the order and become a composer in the court of the Duke of Mantua and Monferrato.

He became a deacon in 1692, the same year he achieved the post of organist at Santa Maria dei Servi in Bologna.

After enjoying the favor of the Queen, Ariosti wrote and collaborated in the writing of a number of stage works performed for the court in Berlin.

Although he could sing, write drama, play the violoncello and harpsichord; his favorite instrument was the viola d'amore, for which he wrote 21 solo sonatas.