And she thinks people will be willing to forgive him.
Winfrey said Monday that the hardest thing Armstrong has done in his life is confess in an interview with her that he used performance-enhancing drugs to win his seven Tour de France titles.
"If he is willing to do the work ... he can be a real hero," Winfrey said during a lecture in Edmonton, the first stop on a speaking tour through Western Canada.
She said Armstrong's fall from grace is so huge, it means a lot that he has finally come clean. But he also needs to realize his life is not just about a bike, races or a big mistake.
"Everybody has the ability within them to rise again. What really matters in the world is what kind of human being he chooses to be."
Oprah's exclusive interview last week with Armstrong was a ratings boon for her specialty channel, OWN: Oprah Winfrey Network. The channel has been struggling and even Winfrey admitted it hasn't been the success she had hoped.
The media maven compared her channel's bad reviews to Armstrong's lost respect. She said she has decided to shift focus and believes her channel will soon get back on track.
"In three years it will be a force for positivity and raising consciousness in the world."
Billed as "An Evening with Oprah," Winfrey easily switched hats between motivational speaker and stand-up comic. She had the crowd of about 15,000 laughing, gasping and nodding their heads.
Organizers said it was Winfrey's first big arena show, and a sell-out to boot.
Unlike the arena's usual hockey crowds, most people there Monday night were women. Many came with girlfriends and some with their moms.
"Oprah's changed a lot of people's lives," said 77-year old fan Jeanine Bussiere, who went to the event with her daughter. She said she used to watch Winfrey's daytime talk show religiously before it went off the air in 2011.
Winfrey gained world-wide fame for her nationally syndicated show, which lasted 25 years. She said it was the best job in the world and the show's legions of fans were like family.
"I have a bunch of children in Edmonton that I have raised," she told the crowd. "Now you have children and I'm raising your children."
Oprah will be speaking in Calgary on Tuesday night and Vancouver on Thursday.