Alley, 60, is best known for her work on TV's "Cheers," "Veronica's Closet" and "Dancing with the Stars," as well as in the "Look Who's Talking" movies.
"I've lost 100 pounds," she told "Entertainment Tonight" in a segment which aired Tuesday.
"I feel like I'm back in my element," she added. "I honestly didn't even realize what I looked like."
UsMagazine.com said the interview was broadcast the same day Alley wowed the audience at designer Zang Toi's runway show during Fashion Week in New York.
"Before 'Dancing with the Stars,' I bought these dresses from size 14 to 4," she told "ET." "[They were] all the same dress, and I said, 'You know what I really want? I really wanna be in this dress in a 4!'"
She said she has since achieved her goal, but did not say exactly how, or what her weight was before she lost 100 pounds.