On Wednesday, Rousey attempted to one-up Mayweather's challenge to "call me" when her earnings match his, telling TMZ Sports she actually earns more per second than he does. Rousey also said in the interview, "When he learns to read and write, he can text me."
Mayweather didn't wait long to fire back at Rousey.
"Big bank take little bank," Mayweather said in a statement that appeared on TMZ Sports. "Let's play and see how much money you got.
"Last time I checked I was No. 1 on Forbes," Mayweather said, referring to the publication's ranking of the world's highest-paid athletes. "She will never be at my status. Keep trying to get publicity."
Mayweather amassed $420 million in earnings in 2015, according to the Forbes list released in June, including nearly $220 million for his May 2 victory over Manny Pacquiao in the richest fight in boxing history.
Forbes estimates Rousey made $3 million from June 2014 to June 2015 in UFC salary.
Rousey's war of words with Mayweather first escalated in July, when she said after winning the ESPY for Best Fighter, for which Mayweather was also a nominee: "I wonder how Floyd feels being beat by a woman for once. I'd like to see him pretend to not know who I am now."
The remarks were made a year after a July 2014 interview with Mayweather, in which he said of Rousey, "I don't even know who he is."
Earlier this month, Rousey said she could beat Mayweather in a no-rules mixed martial arts-style fight in the Octagon.
Rousey (12-0) has dominated the UFC during her reign as female bantamweight champion. She defended her title by knocking out Bethe Correia only 34 seconds into the first round at UFC 190 in early August.
Mayweather (48-0), long rated No. 1 on ESPN's pound-for-pound list, is scheduled to defend his welterweight title against Andre Berto on Sept. 12.