Iglesia de San Juan Bautista, Buenos Aires, Catholic church in downtown Buenos Aires, Argentina.

Iglesia de San Juan Bautista is a Catholic church on the corner of Alsina and Piedras streets in the Monserrat neighbourhood of Buenos Aires, completed in 1797. It has a single nave covered by a barrel vault, a blind dome over the transept, and a facade from 1895 by J. M. Belgrano, later reworked by Rómulo Ayerza, with a central arch, rose window and unequal towers.

The first church was built in 1654 under Fray Cristóbal de la Mancha y Velazco; after it fell into ruin, Juan Bautista de San Martín funded a replacement, raised in 1719. It was rebuilt in 1767 and demolished in 1778, and the present building was finished in 1797. In 1942 it was declared a National Historic Monument.

The church is also called "San Juan de los franceses" because Buenos Aires' French community worshipped here in the late 19th century, devoted to an image of Saint Bernard. It was known as the "church of the Basques" through the Betharramite priests, called "bayoneses", who ran it and worked among the Basque community. In the Patio de los Capellanes stands a statue of Saint Clare, credited with the city's Reconquest of 1806.

The church stands at the corner of Alsina and Piedras streets in Monserrat, a few blocks from Plaza de Mayo and the Avenida de Mayo subway line. Enter from Alsina; the Patio de los Capellanes, with its statue of Saint Clare, is reached beside the church. The Patio de la Reconquista lies in the parish house courtyard and is not always open.

The crypt under the choir holds the tombs of 270 Capuchin Poor Clare nuns, not 260. The same church keeps the sepulchre of Pedro Melo de Portugal y Villena, fifth viceroy of the Río de la Plata, and in the parish courtyard called Patio de la Reconquista lie criollo and English soldiers killed in the 1806 and 1807 invasions.