Fortaleza de Nossa Senhora da Conceição, Military fortress in Saúde district, Rio de Janeiro, Brazil.

Fortaleza de Nossa Senhora da Conceição stands on the Morro da Conceição in Saúde, Rio de Janeiro, on the site of a battery raised by French corsair René Duguay-Trouin during the 1711 invasion. Completed in 1718, it held 36 guns and 1,000 shot of various calibres, the city's third-largest artillery after Santa Cruz and São João. Its buildings include a chapel, the Casa das Armas and workshops.

The fort was built from 1711 to 1718 after French corsair René Duguay-Trouin took Rio in 1711; engineer Jean Massé planned it and it was finished in 1718 with 36 guns. From 1791 it held Inconfidência Mineira prisoners such as Tomás Antônio Gonzaga, and in 1798 some Conjuração Baiana members. Disarmed in 1831, it later served as a prison and since 1930 has housed military geography services.

The fort's name comes from Nossa Senhora da Conceição, and a chapel of that invocation stood within the walls. In 1718 the bishop of Rio, Dom Francisco de São Jerônimo, complained that the fort's salutes shook the neighbouring episcopal palace; the Crown ordered a silver lamp worth 130,000 cruzados for the chapel and restricted the firing of salutes.

The fort now houses the 5th Geoinformation Center, and its historical library is open to the public. The site sits on elevated ground in Saúde, so allow time for the climb and wear sturdy shoes. Access to the library may require confirming opening hours in advance.

One of Rio's earliest organized labor protests took place here in 1791 when workers demanded their delayed wages. The moment marks the beginning of the city's labor movement and shows how this military site was also a stage for social unrest.