Guillermo Gregorio (born May 1, 1941, Buenos Aires) is an Argentine jazz and free improvisation clarinetist, saxophonist, and composer.
Around early 2016, he moved from Chicago to New York City, where he lives and works today.
In 2001, he founded the Madi Ensemble, with whom he further developed Argentine avant-garde styles.
He previously taught at Purdue University and had a work commissioned by the Chicago Symphony Orchestra.
In 2001, Gregorio worked with a string quartet and the trombonist Sebi Tramontana.