The former "Fashion Police" co-host will join Junior hosts Tim Gunn and supermodel Hannah Davis for the series, which will invite kid designers aged 14 to 17 to show off their best work, reported Us magazine.
She will judge the series alongside fashion designer and former "Project Runway" winner Christian Siriano.
"I'm so excited to finally announce that I've joined the incredible Project Runway Junior family!. We just had the best first day ever!," she said.
Osbourne, 30, teased fans earlier by posting a photo of herself hiding out at Mood Fabrics, the New York City and Los Angeles garment shop where "Project Runway" designers purchase items for their challenges.