It happened just after 2 a.m. near the 710 Freeway near 7th Street, officials said.
A preliminary investigation indicates a car was headed northbound on the freeway when it rear-ended the Long Beach Fire Department ambulance before hitting the center median.
There were two people inside the car. A female passenger was pronounced dead at the scene, while the driver, 27-year-old Christian Castillas, was taken to the hospital for treatment of his injuries.
No one inside the ambulance was injured.
Officials said speed and intoxication appear to be factors in the crash.
As a result, Castillas was arrested on suspicion of felony vehicular manslaughter while intoxicated and felony driving under the influence causing bodily injury. His bail was set at $100,000.
Long Beach police urged anyone with information about the crash to call them at 562-570-7355.