The K-1 World Grand Prix in Hawai'i is already considered a big event in the sport of mixed martial arts.

In the martial art of jiu-jitsu, the main event featuring Hilo's BJ Penn against Brazil's Renzo Gracie is huge.

"I think this might be the biggest fight in the history of jiu-jitsu," Penn said.

Penn is Hawai'i's biggest star in mixed martial arts. He is a second-degree black belt in jiu-jitsu, and is the only American ever to win a jiu-jitsu black belt world championship.

Many fight publications and Web sites rank him as the best "pound-for-pound" fighter in the world.

Gracie is one of the most famous family names in mixed martial arts. Like several other family members, Renzo is considered a jiu-jitsu master. He is a fifth-degree black belt.

Penn and Gracie will be in one of the "Super Fights" of the 14-bout card tomorrow at Aloha Stadium. There are no championship belts on the line, but as Penn put it: "Titles mean nothing in a fight like this."

Gracie added: "Every jiu-jitsu guy is talking about this fight. The reason why I took this fight is because I'm not 100 percent sure I am going to win. If I was 100 percent sure I could win, I wouldn't take it. BJ is a very strong fighter, complete in every aspect. This is such a challenge to me that I couldn't do anything but embrace it."

The bout will follow mixed martial arts rules and both fighters are expected to make the 185-pound weight limit.

Penn is 26 and has a professional record of 9-2-1. Gracie is 38 and has a record of 10-5-1, but has not fought since October of 2003 because of a knee injury. He said the ruptured anterior cruciate ligament in his left knee is fully healed.

"There's some history between us," Penn said, and he was not even referring to his victory over Rodrigo Gracie — Renzo's cousin — last year.

Early in his career, Penn trained in California under Ralph Gracie, who is Renzo's brother. Ralph will be coaching from Renzo's corner tomorrow.

"That was a long time ago and we've gone our separate ways since then," Penn said. "We don't even talk any more, but it's not like there's bad blood or anything."

Renzo Gracie said of Penn: "I think the fact that he trained under my brother gives him an advantage because I know that he learned jiu-jitsu the right way. I'm sure me and my brother will exchange knowledge, but I don't know if that makes a difference."

Gracie said his return to the fighting ring has nothing to do with family revenge.

"I think that's media hype," Gracie said. "I have nothing against BJ."

In any case, Penn said he does not expect the bout to go straight to the canvas and turn into a jiu-jitsu match.

"It probably makes it harder for both of us knowing each other's styles," Penn said. "But I have to assume he's the best striker, the best wrestler. I have to be ready for everything and go in there and just scrap."

Penn is currently involved in an assault charge against a Honolulu police officer, but he said the ongoing case will not affect his performance.

"Of course, I can't comment on any of that," he said. "But when ever I step in the ring for a fight, everything else in my life is put aside for the fight."