The 28-year old international joins the North London club from the Super Lig champions where he has made 52 league appearances, scoring ten times.
The former Corinthians player received his first ever senior cap for Brazil at the 2009 Confederations Cup and has gone on to make 22 appearances for the national side.
Arsene Wenger, who has recently been under pressure because of the lack of signings, believes Santos can provide the squad with a different dimension.
Wenger told the club’s official website: “Santos is a quality player, with the ability to both defend well and get forward and help with attacks.
“He has experience in the Champions League and for Brazil and has he can deliver at the highest level.
“We welcome Santos to the club and look forward to seeing him play here.”
Santos has been the subject of speculation throughout the summer with PSG and Porto interested. Following Fenerbache’s expulsion from the Champions League, Santos knew moving to Arsenal would be the right thing for his career.
Santos said: “I am delighted to have signed for Arsenal. It was one of my dreams to play for a major European football club and I have accomplished this.
“I am very happy to be part of the team. All the Brazilians who came to this club spoke wonders about it and I am delighted to be part of the Arsenal family.”
Santos is not the only player to be moving to the Emirates today with German Per Mertesacker expected to complete his move tonight.
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