Flight QZ8501 vanished from radar screens over the northern Java Sea on Dec. 28, less than half-way into a two-hour flight from Indonesia's second-biggest city of Surabaya to Singapore. There were no survivors among the 162 people on board.
"We've found the tail that has been our main target today," Fransiskus Bambang Soelistyo, the head of the search and rescue agency, told a news conference in Jakarta.
The tail had been identified using an underwater remote operated vehicle, Soelistyo said, adding that the team "now is still desperately trying to locate the black box".
Forty bodies and debris from the plane have been plucked from the surface of the waters off Borneo, but strong winds and high waves have prevented divers from reaching larger pieces of suspected wreckage detected by sonar on the sea floor.
An Indonesian naval patrol ship captain had said on Monday that his vessel had found what could be the tail, but there had been no confirmation of the find.
Locating the tail has been a priority because the cockpit voice and flight data recorders crucial for investigators trying to establish why the plane crashed are located in the rear section of the Airbus A320-200.