The Italian coach heaped praise on the Real Madrid captain but stressed he has not been brought to the club as a peacemaker following Jose Mourinho's exit.
Casillas was consigned to the sidelines after a falling out with Jose Mourinho in the latter part of last season, but the club's new coach has made it clear he will restore the Spain skipper to the side if he proves his worth.
"Casillas is a great player," the former PSG boss told reporters at a press conference. "He has won everything. But the rules of football are what they are: if he deserves it, he will play."
Napoli boss Rafa Benitez hinted that Ancelotti would be able to "restore the values" at the Spanish capital club after Mourinho's turbulent final few months, but the Italian does not view himself as peacekeeper.
“I’ve never been called that," he continued. "I’m simply a coach who wants to have a good relationship with his players. But I don’t think Madrid need a ‘peacemaker’. It’s a nice word, though, so thanks.
"But Mourinho is a great coach. I respect him a lot. Each person has their own character, so it's not good to make comparisons with Mourinho. When I'm finished, the president will tell whether I have done better or worse [than Mourinho]."
There has been talk that star player Cristiano Ronaldo could leave Madrid this summer, amid talk of a possible return to Manchester United, but Ancelotti is under the impression that he will be given the opportunity to work with a talent that he admires greatly.
"Ronaldo is a fantastic player; wonderful," the 54-year-old enthused. "It is an honor to coach a player like him."
Ancelotti has signed a three-year contract with Madrid, having parted company with Paris Saint-Germain.