The Italian coach heaped praise on the Portuguese superstar and stressed he has not been brought to the club as a peacemaker following Jose Mourinho's exit
The Portuguese winger has been consistently brilliant since arriving from Old Trafford for £80 million in the summer of 2009, but appeared unsettled at times last season.
Reports in Spain have suggested Ronaldo is set to meet with United officials to discuss a possible return, but Ancelotti has turned on the charm on his unveiling as Madrid boss.
"Ronaldo is a fantastic player, wonderful," he told reporters. "It is an honour to coach a player like him."
Ancelotti also lavished praise on Iker Casillas, but warned he will need to earn his Real Madrid starting berth back after falling out of favour under Jose Mourinho.
"Casillas is a great player," the former PSG boss added. "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]."
Ancelotti has signed a three-year contract with Madrid, having parted company with Paris Saint-Germain.