Martinsville Sanitarium is a historic mineral water sanitarium located at Martinsville, Morgan County, Indiana. It was built in 1925–1926, and is a 2+1⁄2-story, "oriental brick" and limestone building with an eclectic combination of Tudor Revival, Colonial Revival, Renaissance Revival, and Bungalow/American Craftsman style design elements. The main section measures 160 feet by 55 feet and has two projecting wings. It is topped by a cross-gabled hipped roof and features a sun porch, half-timbered gables, and overhanging eaves. The building faces the Martinsville Vandalia Depot.

It was listed on the National Register of Historic Places in 2005.