Uruguaiana is a municipality in the Brazilian state of Rio Grande do Sul. It is located on the left-hand (eastern) shore of the Uruguay River that forms the border with Argentina. Opposite Uruguaiana, and joined to it by a road/railway bridge, lies the Argentine city of Paso de los Libres, Corrientes. North of Uruguaiana lies the Brazilian town of Itaqui, connected by a bridge constructed by the English in 1888 over the Ibicuí River. The municipality also borders the municipalities of Alegrete, Barra do Quaraí and Quaraí, and, also, Uruguay, making it one of the few international triple-border municipalities of Brazil.
The city marks the southernmost point reached by the Paraguayans in the Paraguayan War; after being taken without resistance, it was recaptured after a six-week siege that effectively ended the phase of Paraguayan offensive operations.
Nowadays, Uruguaiana represents the biggest in population and arguably most important municipality of the sparsely populated western Rio Grande do Sul.