The Roman Catholic Archdiocese of Bahía Blanca (Archidioecesis Sinus Albi) is a Latin Metropolitan archdiocese of the Roman Catholic Church with an ecclesiastical province in the eastern region of the national capital's province of Buenos Aires, central Argentina.

Since 12 July 2017 Carlos Azpiroz Costa has been its Archbishop.

As per 2015, the Archdiocese pastorally served 661,096 Catholics (83.3% of 793,517 total) on 82,624 km² in 55 parishes and 236 missions with 71 priests (45 diocesan, 26 religious), 27 deacons, 211 lay religious (44 brothers, 167 sisters) and 15 seminarians.

It covers the partidos (municipalities) of Adolfo Alsina, Adolfo González Chávez, Bahía Blanca, Coronel Dorrego, Coronel de Marina Leonardo Rosales, Coronel Pringles, Coronel Suárez, Daireaux, Guaminí, Monte Hermoso, Patagones, Puán, Saavedra, San Cayetano, Tornquist, Tres Arroyos and Villarino.

The Metropolitan Archdiocese has suffragan sees encompassing all of the administrative Provinces of Patagonia and Tierra del Fuego, notably : (all Roman Rite)