Students at the event said they appreciated the message, although some expressed doubt about whether the fighters were the best people to deliver it.
"They should and they should not be presenting this because their job is violent," said 13-year-old Jerrell Halladeen.
"So kids our age are going to take that as hypocrisy, but it is their job to do that, so what they do is right."
The event at the Rogers Centre comes amid heightened awareness of the damage bullies inflict, leading to several highly publicized teen suicides in recent months.
Capitalizing on their popularity, four UFC fighters pressed the students to look out for one another, to report bullying to authorities, but most of all, to understand its effects.
The fighters pointed out that their sport takes place in a controlled atmosphere among willing and matched competitors, and bears no resemblance to the school yard or workplace.
UFC lightweight Sam Stout dismissed suggestions of hypocrisy, saying their sport was not about the "meanest tough guy" coming out on top.
Instead, Stout said, it's the best trained athlete and "smartest fighter" who wins.
"That's not the driving force: to hurt somebody," said Stout, a native of London, Ont. "The driving force is to be the best at what we do."
On Monday, Toronto city councillor Doug Ford, brother to Mayor Rob Ford, raised eyebrows when he said the UFC fighters were ideal anti-bullying ambassadors because many kids idolize them.
Some trustees considered his endorsement irresponsible.
But UFC welterweight Sean Pierson of Pickering, Ont., said he didn't get the criticism.
"I don't understand why it's any different for me speaking about it rather than my dad, who worked at IBM," Pierson said.
"It's not a contradiction: This isn't about fighting, what I do, this is about competing ... against another combatant that's been trained to do what I do."
Pierson urged students to set goals and make the right decisions early in their lives.
It was important, he said, to get a dialogue going among students the harm bullies do.
"It's more the emotional abuse and emotional problems that happen when kids are bullied than the physical," Pierson said.
"You don't see too often that kids physically get beaten up so bad that that's the problem."
UFC fighters are sports celebrities in their own right and lure countless viewers to TV screens and big-ticket events around the world.
The event was sponsored by the city's police service and the Ultimate Fighting Championship, the world's largest mixed martial arts promoter.
UFC 140 is set or Saturday at Toronto's Air Canada Centre.
One part of Tuesday's event that appeared to really strike home was the showing of a video that's gone viral called "What's Goin' On" by John Mowry.
In the video, Mowry, who is in the eighth grade, sheds tears as he talks about being bullied and battling depression.
"It was great to show how bullying affects other people's lives and feelings," said Darnell Richards, 13.
Also on Tuesday, Ontario Premier Dalton McGuinty said students would be able to set up gay-straight clubs to promote tolerance in public schools under new anti-bullying legislation.
Some Catholic schools have banned the alliances, but McGuinty said the bill specifically would allow the groups.