Speaking at the National Radio conference in Sydney, the former X Factor judge said that his fans will soon grow tired of him because he "still looks like that little boy".
"For me, Justin is... I've met him, I've worked with him, I did a TV commercial with him. He's a really great little guy. But that's his problem - he's a little guy," Osbourne said.
"His fans are growing up, they're 18, 19-year-olds now. And that means the little girls of titties and lips (sic), you know they're young women. And he still looks like that little boy! He needs some hair, or something.
"I just don't think, from my gut, maybe my gut's wrong 'cos it's not 100%, but I don't think he's going to stand the test of time.
"But you know what, I don't feel sorry for him, because he's made oodles and he's a fabulously nice person and he'll go on to do something else."
Osbourne recently admitted that she would "love" to return to The X Factor as a judge.
Watch Justin Bieber's new video for 'Beauty And a Beat' featuring Nicki Minaj below: