Alves was found guilty in February 2024 of raping a woman in a nightclub in December 2022 and sentenced to four years, six months in prison.
The former Brazil and Barcelona defender denied wrongdoing during the three-day trial.
That court ruled on Friday that there was "insufficient evidence" to rule out Alves' presumption of innocence.
"Dani Alves is innocent, and that has been proven," his defence lawyer Ines Guardiola told Catalan radio RAC1. "Justice has finally been served."
The Alves trial was the first high-profile case since Spain overhauled its laws in 2022 to make consent central to defining a sex crime in response to an upswell of protests after a gang-rape case during the San Fermin bull-running festival in Pamplona in 2016.
The legislation popularly known as the "only yes means yes" law defines consent as an explicit expression of a person's will, making it clear that silence or passivity do not equal consent.
But the four judges of a Barcelona-based appeals court ruled unanimously to overturn the conviction after reviewing the evidence and testimonies given to the lower court.
In their ruling, they wrote that the testimony of the plaintiff "differed notably" from evidence of video footage taken before the woman and Alves entered the bathroom where she said he forced her to have sex without her consent.
Alves, now 41, was kept in jail from January 20, 2023 until March 2024 until he was released after paying one million euros for bail while awaiting his appeal.
Alves was one of the most successful players of his generation, winning three Champions Leagues and six Spanish league titles when at Barcelona, while helping Brazil win two Copa Americas and an Olympic gold.
He was with Mexican club Pumas when he was arrested, and had his contract terminated immediately.
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