Janice Xu, 10, suffered a medical emergency, possibly cardiac arrest, while on Delta Flight 2423 from LAX to Seattle on Thursday night.
The plane turned around while still over Southern California and landed at LAX. Paramedics were unable to revive the girl and she was pronounced dead.
Officials say there are no immediate indications of anything suspicious in connection with her death.
The Los Angeles County Coroner's Office expects to perform an autopsy within the next day or two.