Song says he hopes there are no hard feelings from Arsenal over his decision to leave.
He told Barca TV: "Today is a very good day for me and my family. Very happy to be here, this is the best team in the world, playing at a club like Barça is something I wanted when I was young.
"I hope the team will continue to win, this is a winning team. They win everything. I will give my best on training and when I get the chance to play I will do it.''
"I know Cesc very well, I slept at his house last night,'' he added. ''He's a very good friend of mine, he will help me to integrate.''
After passing his medical with flying colours, doctor Ricard Pruna said of Song: "His body fat percentage is extremely low and he has good muscle quality.
"I don't think he's had muscle injuries since he was 17, and that's really good news. He passed all the tests and he's available to the manager."