The late night TV host was recently rumoured to have been approached for the gig by outgoing Academy of Motion Picture Arts & Sciences president Tom Sherak.
However, Fallon revealed that he turned down the hosting gig, hinting that he may take it on in the future.
"No, I'm not going to do the Oscars," he told Today's Matt Lauer.
"It's an honour to be asked by the Academy, but it's not my year."
Lorne Michaels was said to have been in line to produce next year's ceremony with Fallon.
The Oscars currently air on ABC, and Fallon's titular Late Night talkshow airs in competition with its own Jimmy Kimmel Live!, which may have caused a conflict for the network.
The 85th Academy Awards will take place on February 24, 2013 at the Dolby Theatre (formerly the Kodak Theatre).