Lorenzo Masi, known as Lorenzo da Firenze (Magister Laurentius de Florentia; died December 1372 or January 1373), was an Italian composer and music teacher of the Trecento.

He was closely associated with Francesco Landini in Florence, and was one of the composers of the period known as the Italian ars nova.

He became a canon at the church of San Lorenzo in 1348, a post which he retained for the rest of his life.

In addition to his contribution to that collection, he wrote two mass movements which have survived (one of which is of doubtful attribution) and a pedagogical piece (the Antefana), the text of which shows that he was a teacher.

In addition he used chromaticism to a degree rare in the 14th century, at least prior to the activity of the composers of the ars subtilior.