The 26-year-old "Nashville" star developed the disorder after the birth of her daughter Kaya in December 2014 and had sought help for the first time seven months ago, reported Ace Showbiz.
Panettiere announced her second treatment via Twitter.
"The postpartum depression I have been experiencing has impacted every aspect of my life," she tweeted.
"Rather than stay stuck due to unhealthy coping mechanisms I have chosen to take time to reflect holistically on my health and life. Wish me luck!"
The actress has been very open and vocal about her postpartum depression.