It's the group's first Grammy win. They're up for four other awards.
``Fun.'s 'We Are Young' wins song of the year Grammy It has sold more than six million single tracks.
Lead singer Nate Ruess joked onstage: ``This is in HD, everyone can see our faces and we are not very young.''
The group is nominated in all four top categories at Sunday's ceremony. They also performed their latest single, ``Carry On,'' at the show.
The Black Keys' Dan Auerbach and Skrillex lead in winners so far with three wins each.