The once-mighty presidential aide was long seen as the real power running the North African country after his brother suffered a debilitating stroke in 2013.
But he was detained in May 2019, a month after Bouteflika quit office following mass protests against his bid for a fifth term.
Said was sentenced with two former intelligence chiefs and a Trotskyist politician to 15 years in prison for "plotting" against the army and the state, and in February, a military court upheld that ruling.
But in November, the supreme court said they would be retried after appeals.
"After deliberations, the court... rescinded the original ruling and acquitted all the defendants," lawyer Khaled Berghel told APS.
Despite being cleared, Bouteflika remains in custody and will be transferred to another prison as he awaits a separate trial over alleged corruption during his brother's rule, a court official said.
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Bouteflika and three others were accused of meeting in March 2019 and plotting to derail plans by the army high command to force the departure of Abdelaziz Bouteflika.
Said Bouteflika allegedly wanted the intelligence bosses to dismiss the army chief of staff at the time, General Ahmed Gaid Salah.
His co-defendants included General Mohamed Lamine Mediene, known as "Toufik", who headed the powerful Department of Intelligence and Security for 25 years.
Also on trial were Louisa Hanoune, who had served as secretary general of the Workers' Party, and General Athmane Tartag.
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