The "Batman v Superman" star admitted in his post that addiction is "something I've dealt with in the past and will continue to confront."
The 44-year-old actor, director and Oscar winner also went to rehab back in the early 2000s.
"I want to live life to the fullest and be the best father I can be," he said in his post today. "I want my kids to know there is no shame in getting help when you need it, and to be a source of strength for anyone out there who needs help but is afraid to take the first step."
"I'm lucky to have the love of my family and friends, including my co-parent, Jen, who has supported me and cared for our kids as I've done the work I set out to do. This was the first of many steps being taken towards a positive recovery," he added.
In 2001 when Affleck first entered rehab, his rep David Pollick told ABC News via statement, "Ben is a self-aware and smart man who has decided that a fuller life awaits him without alcohol. He has chosen to seek out professional assistance and is committed to traveling a healthier road with the support of his family, friends and fans."