Álvaro Xavier de Castro (Portuguese pronunciation: [ˈalvɐɾu ʃɐviˈɛɾ ðɨ ˈkaʃtɾu]) was Prime Minister of Portugal from 20 November to 30 November 1920 and from 18 December 1923 to 6 July 1924.

He was part of the Constitutional junta that governed Portugal in 1915.

He was a prominent participant in the attempted coup of 11 January 1919 which took place after the assassination of Sidónio Pais.

[citation needed] De Castro co-founded the National Reconstitution Republican Party.

He again became Prime Minister of Portugal, from 18 December 1923 to 6 July 1924.