Alba posted a video and a picture of her transformation on her Instagram page.
She captioned the photograph: "This happened. Thanks Chad Wood hair for the awesome haircut. It feels sooo good to shed the pregnancy hair. Whaddaya think?"
Alba, who also has daughter Honour, nine, and Haven, six, with her husband Cash Warren, felt like she needed a new look after welcoming her third child, a son.
She chopped the inches off her hair with the help of celebrity hair stylist Chad Wood, who also posted a video of the transformation to his social media page.