BastiaSong joined the Bastia youth team in 2003-04 and became a part of the first team the following season with 34 appearances. During his time at Bastia, he attracted attention from numerous clubs, including Inter, Manchester United, Lyon, and Middlesbrough.However, he impressed Arsenal manager Arsène Wenger as a trialist during Arsenal's pre-season training camp in Austria, and Arsenal secured his services on loan for the 2005-06 season. Arsenal agreed to a £1 million fee in June 2006 and signed him to a four year contract.
ArsenalSong made his Premiership debut during Arsenal's 2-0 win against Everton F.C. on September 19, 2005 as a substitute. He played in several Champions League matches and made several Premiership starts near the end of the season, when players like Cesc Fàbregas and Gilberto Silva were injured or being rested.
He scored his first goal for Arsenal against Liverpool in Arsenal's 6-3 win at Anfield in the League Cup on January 9, 2007.
On January 30, 2007, it was confirmed that Charlton Athletic had signed Song on loan until the end of the 2006-07 season.Although he impressed, Charlton were relegated and Song returned to Arsenal.
Over the 2007-08 season, Song started at centerback for Arsenal's Carling Cup matches, but missed their semifinal elimination by Tottenham while away with Cameroon at the Africa Cup of Nations. He also started at centerback in Premier League ties towards the end of the season, most notably in Arsenal's crucial visit to Old Trafford against Manchester United, while regular starter Kolo Touré filled in for Bacary Sagna at right back and Philippe Senderos was emotionally shaken by Arsenal's quarter-final exit from the Champions League.