The Castle of Viana do Alentejo (Portuguese: Castelo de Viana do Alentejo) is a gothic castle constructed during the reconquest and settlement of the central region of the Portuguese Alentejo, located in the parish of , municipality of the same name. Although a relatively low-profile design, in comparison to its contemporaries (such as the Castle of Portel or Castle of Feira), the structure served the period of strife associated with expansion of Portuguese forces/authority into the southern Algarve.