Plácido de Castro (Portuguese pronunciation: [ˈplasidu dʒi ˈkastɾu]) is a municipality located in the east of the Brazilian state of Acre on the border with Bolivia.

José Plácido de Castro, who was prefect of the Alto Acre department in 1906–07, recommended the need for a settlement to stabilise the situation.

[4] The Plácido de Castro District is shown as part of the Rio Branco municipality in the divisions of 31 December 1936 and 1 July 1960.

The local economy is based on beef and dairy cattle, saw mills, furniture manufacture, tourism, agriculture and extraction, particularly Brazil nuts.

The neighbouring Bolivian village of Vila Montevidéu had a free trade zone for imported goods that was much visited by Brazilians.