Adesanya, 31, easily defended his UFC middleweight title against Costa at UFC 253.
'The Last Stylebender' is quickly becoming one of the sport's biggest stars and former UFC champion St-Pierre believes he's a "perfect fighter."
Speaking to ESPN, he said: "(Israel Adesanya's) amazing. He's a perfect fighter.
"We're in the entertainment business, and our job is to entertain the audience, and he's doing it very, very well."
St-Pierre has previously called UFC lightweight champion Khabib Nurmagomedov the best fighter on earth.
In August, he told BT Sport: "Khabib right now, I believe, is the best fighter on the face of the Earth.
"On the face of the planet, he is the best right now."
The Canadian megastar continues to flirt with the idea of returning to the famed Octagon and insists he only wants to face Nurmagomedov if he does return to action.
"If I ever come back, I'm not coming back for many fights," he added.
"If I come back, it would be for one fight. And I need to take, for me, the biggest fish. And the one - for me, I believe - the top guy right now, the name is Khabib.
"As a fighter, the most exciting thing is to take the guy who seems invincible, unbeatable. He has the aura of invincibility. But it's also the scariest thing to do."
The 39-year-old hasn't fought since capturing the UFC middleweight title against Michael Bisping at UFC 217 in November 2017.
Will he step foot back inside the cage? Watch this space.
Featured Image Credit: PA/YouTube
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