The America's Got Talent judge said that she believes her 26-year-old son has the right attitude to "conquer" the degenerative illness.
Speaking on Conan O'Brien's TBS chat show, she declared: "He is actually doing amazing, he is so strong and positive. My son will conquer!"
Sharon also revealed that the family had kept the condition to themselves for a month. Jack and Sharon shared the news in a recent magazine interview.
Adrenaline junkie Jack, who has already thanked fans for their support, confirmed that he discovered his MS following an appearance on a reality show.
Multiple sclerosis affects the nervous system and impairs muscle control and strength, impairing balance, vision and brain function. Cases vary, and it remains unclear what stage Jack's MS has reached.
Watch Sharon Osbourne discuss Jack Osbourne on Conan below: