The Italian coach has managed some of the biggest names in football throughout his 18-year career as a boss, but he feels that the Portuguese star is the finest of the lot.
"[Ronaldo is] the best I've ever seen," Ancelotti told The Times.
"He's scored in every game in this period — 25 goals in 18 games — and he can score more.
"I've seen Ronaldo play a lot of times, of course, but when you're up close every day his technical skills are unbelievable."
Los Blancos are currently third in La Liga.