KHLOE KARDASHIAN OWES OVER $18,000 IN BACK TAXES!

Khloe Kardashian's officially got bigger back than Kim ... taxes, that is -- at least according to the State of California.

According to a new tax lien filed Friday -- obtained by TMZ -- Khlomar's female half owes $18,490.74 to the Golden State.

It's allegedly all from 2007 -- the same year she launched her career on "Keeping Up with the Kardashians."

Khlo's reps couldn't be reached for comment.