The 33-year-old has already scored five goals and set up four in nine appearances in the Italian top flight despite a slow start following his summer switch from Real Madrid.
The Portuguese star has been tipped to help Juve end their long search for a Champions League crown and enhance the Turin side's hold on the domestic title.
And, although Ancelotti is happy to see Serie A have another global icon, he wonders if his former player could have picked a better team.
"The arrival of Cristiano is an excellent sign for the image of Serie A," he told France Football.
""For a long time, it was the league of stars, Diego Maradona, Michel Platini, Zico, Zinedine Zidane, Ronaldo, Andriy Shevchenko, Kaka, Ibrahimovic... That was the case for at least 10 years. The arrival of Cristiano will restore its reputation.
"He is a huge professional. His only mistake is going to Juve!"
Napoli face Ancelotti's former side Paris Saint-Germain in the Champions League on Wednesday. Although he sees Thomas Tuchel's team as one of the favourites to win the competition, he has confidence in the strength of his own squad.
"It's nice to see how the club is growing," he said. "They are one of the best teams in Europe. PSG can win the Champions League, that's for sure."
He added: "Today is a different Napoli. We do not have Maradona, but we built a real high-level team, with young players in particular.
"Napoli have been playing very well for several years, so the quality is there. I will try to bring some experience, help the team to have a little more personality and courage in some moments when we're not playing as well."