A professional MMA fighter from 2000 until 2009, Arona competed in PRIDE Fighting Championships, RINGS and was a member of Brazilian Top Team.

Arona has notable wins in both MMA and submission grappling competition over Tito Ortiz, Jeff Monson, Renato Sobral, Vitor Belfort, Mark Kerr, Kazushi Sakuraba, Wanderlei Silva, Dan Henderson, Alistair Overeem, Murilo Rua, Jeremy Horn, Guy Mezger, and Dean Lister.

Ricardo overwhelmed him with punches and takedowns, while Kanehara repeatedly reversed to top position and kept attacking, but Arona shockingly submitted him in the second round with a Kneebar.

Afterwards, Arona took part in a tournament for the RINGS Middleweight Championship, facing Jeremy Horn again in the first round and beating him by unanimous decision.

The two contenders fought a series of battles on the clinch, in which Arona imposed his superior wrestling, and almost finished the fight with a rear-naked choke and an Achilles lock at the end of the first round.

The match went back and forth, with Murilo escaping from sparse submissions and landing his famed strikes, but Arona overpowered him with takedowns and kicks at the end and won the unanimous decision.

[citation needed] The victory over Rua was followed by Arona's first defeat in PRIDE, losing his fourth fight to Quinton Jackson in a spectacular knockout.

After the bout, Arona protested and claimed that an illegal headbutt he received by Jackson at the end of the slam was what knocked him out but it was never officially acknowledged or investigated.

He won his first fight in the tournament against Dean Lister by unanimous decision, controlling the ADCC contender in a slow grappling contest.

[citation needed] In the second round of the Grand Prix, Arona won, in controversial fashion, his fight against the Japanese fighter Kazushi Sakuraba via corner stoppage.

He was declared the winner when Sakuraba's corner called a stop to the fight at the conclusion of the second round due to the amount of damage he had sustained.

Arona got a decisive takedown at the second round and performed ground and pound, only for Silva to reverse and get free, which forced Ricardo to pull guard.

At the final round, Arona managed to take Wanderlei to the ground and attack from top position, with Silva reversing him again and kicking at his legs.