The lack of official interest in determining if war crimes were committed during the war and afterwards "is a slap in the face" of families of the missing, Esteban Beltran, director of the Spanish branch of the human rights organization, said in a statement.
Beltran said Spanish authorities had refused to open an investigation into possible violations of international law by both sides in the civil war (1936-39) and under the subsequent rule of Francisco Franco, who died in 1975.
Amnesty International said Spain also was not cooperating with investigations by other countries, such as Argentina.
The Spanish National Court in 2008 ruled it didn't have jurisdiction to hear complaints about killings and the disappearances of 114,000 people committed from 1936 to 1941. It deferred the cases to regional courts.
In 2012, the Spanish Supreme Court said the crimes couldn't be prosecuted because an amnesty law covered them and the period in which they could be tried had expired.
Authorities also prevented victims from testifying before an Argentinean judge.