The body's Digital Music Report 2012 - which takes into account 12-month sales to November 2011 - shows that the singer's Just The Way You Are sold 12.5 million units across the globe, whilst Mars' Grenade shifted 10.2 million in the year.
According to IFPI data*, the world's top-selling digital singles of 2011 were:
Bruno Mars - Just The Way You Are (12.5m)
Bruno Mars - Grenade (10.2m)
LMFAO - Party Rock Anthem (9.7m)
Jennifer Lopez - On The Floor (8.4m)
Adele - Rolling In The Deep (8.2m)
Lady Gaga - Born This Way (8.2m)
Pitbull ft. Ne-Yo, Afrojack & Nayer - Give Me Everything (8.2m)
Black Eyed Peas - The Time (Dirty Bit) (7.3m)
Maroon 5 - Moves Like Jagger (7.0m)
Bruno Mars - The Lazy Song (6.5m)
* Source: IFPI, 12 months to November 2011. Sales are rounded. Combines all versions of the same song.