Katherine Heigl’s smile is no longer yellow — she’s given up smoking!

The Grey’s Anatomy star has been desperately trying to kick her cigarette habit after realizing smoking was taking over her life.

“I started smoking when I was 24, because I’m an idiot,” Heigl previously said. “I don’t enjoy it so much now, because I’ve become such a slave to it. I hate planning my life around when I’m getting a cigarette.”

But Heigl has managed to a whole month without a nasty cancer stick — and she’s already reaping the benefits.

“She feels so much better,” a source told Us Weekly magazine.