I live in MA and my daughters father lives in FL. We were never married and he has been out of the picture since she was born, my daughter is now 6 yrs old. He hasn't paid child support in 5yrs. He has been threating to take full custody of her and wants her to live with him in FL. Now, I'm a hard working mom and going to school to give her the best life possible, and he doesn't work at all. Is it possible that he can do this?

Sure he's allowed to take you to court for custody. That doesn't mean he's going to get it but he can try.

1. is there a court ordered child support order in place.
If there is, have you turned him over to child support enforcement, or taken him back to court for contempt ?

2. He may file for custody, if he lived closer, he may have a chance for joint custody but to take custody away from you, he would have to prove you unfit.