"There are lots of great players in circulation, but nobody is worth as much as him," Ancelotti was quoted as saying in Corriere dello Sport on Thursday.
"Nobody has more determination or is capable of making such a difference in a match. He is better than Ronaldinho."
The 24-year-old Brazilian's hat-trick against Anderlecht on Wednesday took his tally in the Champions league this season to five - the same as Chelsea's Didier Drogba.
He has scored 16 goals in the competition since joining Milan from Brazilian club Sao Paolo as an unknown 21-year-old in July 2003.
According to Ancelotti, it was not only his ability to score that marked Kaka out from his peers.
"Ricky has always scored goals, he's an excellent finisher. But he was not always so good at setting up his team mates," said Ancelotti.
"Now, however, he has improved even that aspect of his game.
"With Kaka in this kind of form, I'm looking forward to seeing who they award the Golden Ball to."
The Golden Ball is the annual prize awarded to the best player in the European leagues.
"Certainly, I would like to win it very much, but I can only do my duty, then hope that I'm rewarded for the results," Kaka said.
"For now, though, I want to play as well as I can for Milan and my national team.
"I don't feel that I've fulfilled my potential yet. There's always something I can improve on".
