Lamonzie-Montastruc (; ) is a commune in the Dordogne department in Nouvelle-Aquitaine in southwestern France. It has two primary chateaux: Le Château de Montastruc, an antique troglodytic site, then a fortress, arranged progressively through its 1500 years of history, and listed as a French Historical Monument; and Le Château de Bellegarde, originating from the 14th Century, although the interiors are of the 20th century.