Neither Ant nor Dec are known to play any instruments professionally. They're primarily known for their work as television presenters and entertainers.
However, they've both dabbled in music on occasion:
* Ant has sung on a few tracks for their charity single "Let's Get Ready to Rhumble", and he's occasionally played the guitar for fun.
* Dec has also sung on some of their charity singles and is known to play the piano.
So, while they may have some musical skills, their main talents are in presenting and performing on stage.