Rousey is preparing for her fight in Brazil against Bethe Correia at UFC 190 on August 1.
In a chat with Yahoo Sports, Tyson said he was impressed with Rousey and felt that she had "that killer aura" about her.
"Ronda is a lady and she's bright, kind, sweet and adorable," Tyson told Yahoo Sports.
"But her whole barometer [as a fighter] is, she's the killer. She has that killer aura, meaning anything is capable of happening. Whoa! That's exciting before the fight even starts."
Rousey said that she was honoured that Tyson had popped around to watch her train.
"It's very humbling and I was just honored that he would go though the trouble or go out of his way to watch me train," Rousey told the Los Angeles Daily News.
Tyson said that he was amazed by her athletic ability and thought she handled herself well.
"All of us are here to see her, and how does she stay focused with all of this?" Tyson said.
"How does she not say, 'I am the s—. I am beautiful. I am a god.' I'm serious. Listen, if you want to become anything close to being a god, the first thing you've got to know how to do is know how to decimate.
"If you're a god, you have to know how to decimate, and that's what she does,” he said.
"It would be very easy for her to have a big head: [Speaking as if he were Rousey], 'I can beat anybody in this world.' I don't know. Maybe she's a likeness of a god," he added.