Lo frate 'nnamorato (Neapolitan: The Brother in Love) is a three-act commedia per musica (a form of opera buffa) by Giovanni Battista Pergolesi, to a Neapolitan libretto by Gennaro Antonio Federico, first performed in 1732.

A successful run was halted by a severe earthquake, which closed the theatres in Naples until the autumn of 1733.

Setting: House of Marcaniello; Capodimonte region of Naples Ascanio, the brother of Nina and Nena, was stolen by brigands in childhood and presumed lost; he was, however, found and adopted by Marcaniello.

Now, Nina and Nena are the wards of their uncle, the Roman Don Carlo.

Finally, in a duel with Carlo, the latter recognizes Ascanio as his lost nephew by a birthmark on his arm.