The 30-year-old, who is engaged to actor-singer Justin Timberlake, said she leaves parties if people's behaviour seems to be getting too wild or out of control, reported Contactmusic.
"If there is a huge drug fest happening and everyone is getting it on in the bedroom, it is probably time to leave," she said.
Biel's said her sensible attitude stems from her teenage years.
"I was lucky to get a part in a long-running TV series, '7th Heaven', when I was 14, and everything took off from there. It was like having two families, my real one and the cast. My mum had me under curfew, so I was well known on TV at the same time as having to be back home early."