Smart spurned the NBA after his freshman year to return to a Cowboys team that was expected to be among the nation's best, but injuries and controversy marred Smart's return.
Big man Michael Cobbins suffered a season-ending injury in late December. In early February, Stevie Clark was dismissed by coach Travis Ford following an arrest. Smart shoved a Texas Tech fan shortly after that and earned a three-game suspension and national scrutiny. Plus, the team endured a seven-game losing streak.
But despite that, Smart told the Oklahoman he didn't regret returning to Stillwater.
"I had a great season here at Oklahoma State," Smart told the newspaper. "It's weird, because I didn't go to the NBA Draft last year, I chose to come back -- which I do not regret at all. A lot of people say I made the wrong decision. But who are they to tell me what I should have done? It's me, not them.
"I believe I made the right decision. I get to do what I love to do."
Smart averaged 17.8 points, 5.7 rebounds and 4.7 assists this season for Oklahoma State, which lost in the second round of this year's NCAA tournament.
"I've told my teammates and my coaching staff, this year was my last year here and I am declaring for the NBA Draft," Smart told the Oklahoman. "I have picked an agent, with the Wasserman Group, a great group of guys.
"Ready to rock and roll. I'm getting ready for the NBA Draft and I'm ready to start training."
Information from ESPN.com's Myron Medcalf contributed to this report.