Adelaide's Zoo's 19-year-old Sumatran tiger Tuan has succumbed to a number of age-related conditions.
Senior veterinarian Ian Smith said Tuan was euthanised on Thursday after it was determined that further treatment would not improve his condition.
"Tuan had been suffering from arthritis and kidney issues which the veterinary team had been monitoring and treating, but over the past week, his health seriously deteriorated," Dr Smith said.
"The team decided there was no additional medical treatment that would have improved Tuan's quality of life and the decision was made to humanely euthanise him."
Tuan was born in 1998 at the Lisbon Zoo in Portugal and arrived in Adelaide in November 2006.
Sumatran tigers are considered critically endangered with fewer than 400 estimated to be left in the wild.