The Opéra du Quai au Foin (French pronunciation: [ɔpeʁa dy kɛ o fwɛ̃]; "Hay Quay Opera") was the first public theatre in Brussels.

Under the aegis of the Governor of the Habsburg Netherlands Alexandre Farnese, Gio-Battista Petrucci, royal historian, and Pierre Fariseau, a notable figure in Brussels society, hired a building on the prairies of the Great Béguinage, on the banks of the Quai au Foin, to a squire.

The first play put on was Egeo in Atene, an opera by Angelo Vitali, followed by several works by Lully.

Abandoned in 1689, the theatre reopened at the end of 1694 under the joint leadership of Gio Paolo Bombarda and Pietro Antonio Fiocco.

It closed for good at the end of 1697 to make room, three years later, for the new "Théâtre sur la Monnoye".