Chai, a 37-year-old Asian elephant transferred from Woodland Park Zoo to the Oklahoma City Zoo last year, died Saturday morning.
She received regular checkups and routine observations from zookeepers and appeared to be healthy.
The average life expectancy for female Asian elephants is 47, and staff at the zoo will be performing a necropsy on Chai to determine why she died so early.
Chai and 48-year-old Bamboo moved to Oklahoma City from Seattle's Woodland Park Zoo in May 2014.
The zoo says Bamboo appears to be healthy and is behaving normally.
FOX25 reports Chai is the second Asian elephant to die at the zoo in the last six months.