"Because Scientologists view children as spiritual beings, you're not treated as a kid," she said in a new clip from the ABC program. "So you're given a lot of responsibility. Your ego becomes extremely inflated."
The actress joined the Church as a young girl at the behest of her mother. She remained with the religion for over three decades.
Now a mother to an 11-year-old daughter, the former King of Queens star also recently revealed how her own child was the catalyst that made her ulitmately leave Scientology.
"I decided I didn't want to raise my daughter in the church because from what I've experienced and what I saw, the church becomes your everything," Remini said in a recent episode of her reality series It's All Relative.
She stressed how exiting the organization meant leaving everything she knew behind. Eventually Leah, her husband and parents all decided to cut their ties with the celebrity-studded faith.
"The decision to leave is your giving up everything you have ever known and everything you have worked for your whole life," she tells 20/20. "I feel that people need to understand this has been my whole life. I want people to understand how it happens."
Leah recants more of her harrowing experiences inside Scientology when 20/20 airs Friday at 10pm on ABC.