"She comes home tomorrow," Douglas told People.com Monday. "She's doing a really good job of getting balanced. I'm proud of her."
The 43-year-old "Chicago" Oscar winner entered treatment last month.
A friend told People.com in April the timing was right for Zeta-Jones to check in for what had always been part of her plan to monitor her mental health.
"This was just a good time to do it. She is in between projects," the friend said, adding Zeta-Jones is "vigilant" about managing her health.
Zeta-Jones announced in 2011 she had the bipolar spectrum disorder, which manifests in abnormally elevated or depressed moods. She said she'd been treated at a mental-health facility in Connecticut but she told ABC's "Good Morning America" in December she was "sick of talking about it because I never wanted to be the poster child for this."