Diaz's camp made the fight announcement Friday evening on its GracieFighter.com website.
The UFC had planned for the lightweight scrap as the main event for "The Utlimate Fighter 8 Finale" on Dec. 13, but a foot injury suffered by Guida pushed the fight back.
Diaz (10-2) has won all five of his UFC fights, and his most recent one, a split decision, was the only fight that didn't result in a submission win. The Stockton native has defeated in the UFC Josh Neer, Kurt Pellegrino, Alvin Robinson, Junior Assuncao and Manny Gamburyan.
Guida (24-6) will look to defeat two straight "The Ultimate Fighter" winners. In his last fight Guida won a unanimous decision over season six winner Mac Danzig.
Current fight card:
170 lbs. | Georges St. Pierre vs. BJ Penn
205 lbs. | Lyoto Machida vs. Thiago Silva
205 lbs. | Stephan Bonnar vs. Jon Jones
170 lbs. | Jon Fitch vs. Akihiro Gono
170 lbs. | Karo Parisyan vs. Dong Hyun Kim
155 lbs. | Matt Arroyo vs. Dan Cramer
265 lbs. | Jake O'Brien vs. Christian Wellisch
155 lbs. | Manny Gamburyan vs. Thiago Tavares
155 lbs. | Nate Diaz vs. Clay Guida