The Italian is convinced the Portguese star will commit his future to the club but remained tight-lipped over negotiations for Gareth Bale
The 28-year-old, whose current deal expires in 2015, has seen his future shrouded in doubt in recent weeks as speculation of a potential return to Manchester United began to surface.
It emerged on Tuesday that the club are preparing to announce the Portugal sensation's new deal after they have finalised negotiations for Tottenham star Gareth Bale, and Ancelotti has voiced his own confidence that Ronaldo will stay at Santiago Bernabeu.
"I am confident Cristiano will renew," he told a press conference. "I think he is comfortable here and I don't think it will be a problem.
"I don't know about a date because that is an issue between the player and the club, but one thing is certain: Cristiano will renew his contract."
The 54-year-old declined to discuss any potential deal for Bale, however, insisting he did not wish to disrespect opposite number Andre Villas-Boas.
"I would rather not speak about it [Bale's transfer] because it would be disrespectful to Andre Villas-Boas," said Ancelotti.
"I do not want to talk about the player. The team is strong, young and I am very happy with the current squad."
The former Chelsea boss will go head-to-head with his old club in the final of the Guinness International Champions Cup on Wednesday, and the Italian admits it will be a "special" occasion.
He added: "It will be a special game. It is normal because I spent two years at Chelsea and had a very good relationship with everyone, and that is special.
"It is a pre-season game, but they are a strong opponent so it will be a good test for us."