The star heaped praise on the mother of four during a recent interview, saying that she's the greatest think about the talent show.
"She's doing a great job on X Factor. We're dead proud. I think she's the best thing on it," Mel C told Digital Spy.
"I just think she's a great woman for the job. She's straight-talking, she's not playing a role. She's just being herself, and I think you have to appreciate her honesty."
But Mel C does admits that she "wouldn't want to be a contestant" while the 39-year-old is on the judging panel.
The two women have developed a close relationship over the years and Mel B recently named the 'I Turn To You' singer as her favourite Spice Girl.
"I'm kind of close to all of them, but I think it [my favourite] would have to be Mel C, 'cause she's from up north, where I'm from," Mel said during an appearance on US TV show Watch What Happens Live.
Mel B currently has two act's left in the competition, Paul Akister and Andrea Faustini.