Prato-Sornico is a former municipality in the district of Vallemaggia in the canton of Ticino, Switzerland.
The municipality contained the villages Prato and Sornico. These entities were former municipalities of their own, having been merged to form Prato-Sornico in 1864.
In 2004 Prato-Sornico municipality was merged with the other, neighboring municipalities Broglio, Brontallo, Fusio, Menzonio and Peccia to form a new and larger municipality Lavizzara.
Prato and Sornico were first mentioned in 1374.
Prato and Sornico, along with Broglio, Fusio and Peccia, formed the valley community of Lavizzara. In 1374, the community dissolved and the villages of Prato and Sornico became independent. The common, shared land of the four communities of Fusio, Peccia, Prato and Sornico (known as the comunella dei quattro comuni) remained shared until 1929. In the 15th Century, the hamlet was the seat of the General Council of the valley, then the seat of the Swiss Confederation governor between 1513 and 1798. After 1803 it was the capital of the sub-district of Lavizzara. Even today stately houses in the village testify of its political and religious importance of the village. One of the houses in the village, which was built in the 15th Century, extended in the 16th Century and renovated in 1975-77, served as the seat of the bailiff and a prison. Another house, in Prato, is Casa Berna which is from the 18th Century. It contains the rich library of Giulio Giovanni Gerolamo Berna, the archpriest of Locarno.