Kayla Harrison Responds To New UFC Champ Julianna Pena's Trash Talk

Kayla Harrison has a message for Julianna Pena -- "don't bite off more than you can chew"  -- after the new UFC champ said the 2x Olympic gold medalist fought in the "B-leagues."

31-year-old Harrison -- the hottest free agent in MMA -- was in the building when ATT gym mate Amanda Nunes shockingly lost her bantamweight title to Pena.

After the fight, Julianna crapped on Kayla, questioning her ability in the cage.

While talking to TMZ Sports on Tuesday, 12-0 Harrison responded ... and it's very ominous.

"I know [Julianna] must be on cloud 9 right now and I would just caution her to be careful. You don't say stuff like that to people like me unless you mean it."

The 3x PFL tourney winner later continued ... "[Pena] went out here and she executed a great game plan and she did what she had to do but I'm not the lesser of anything or anyone or anybody. When I come to fight, you're gonna know you're in a fight and be careful what you say."

At the end of the day, Kayla says the women fight in two different weight classes (JP 135, KH 155) ... so unless Pena's willing to meet in the middle, Harrison believes the trash talk is pointless.

"I think it's just dumb too, ya know? She fights at 135. I fight at, right now, 155, so unless you're willing to back it up, then don't say stuff like that. Don't open that can of worms. Don't go there. Honestly, I'd probably have to chop off my arm to make 135."

"I think that it would only take one arm to beat her."

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If you missed Pena's original comments, here's what she said about Kayla:

“I think she’s the lesser of the training partners for her and Amanda Nunes,” Pena told MMA Junkie earlier this week.

Julianna later said ... “She’s been fighting the B-leagues. I’ve been fighting in the UFC. I’ve been fighting at the top of the division. I’m fighting in the biggest league of this sport, so I’m not paying too much attention to what she’s doing down there.”

We also talked to Kayla about her feelings watching Nunes lose in person (she's "heartbroken") ... and her free agency.

Of course, Harrison's PFL contract just ended ... after again (seemingly easily) winning the $1 million prize.

The former Judo star has been in communication with the UFC ... and is presumably being courted by all the other major MMA promotions.