The pilot was the only one on board when the plane went down in south-central Vietnam, the Ministry of Defense said on state-run television.
The L39 fighter jet belonged to the air force pilot training college near the crash site in coastal Phu Yen province, chief administrator of the provincial people's committee told AFP.
"During its training session, the fighter jet crashed into the rice field, killing the trainee pilot on board," Ho Thi Nguyen Thao said.
Though Vietnam's civilian aviation sector has a strong safety record, there have been several recent accidents involving military aircraft.
In June, a jet fighter carrying two pilots crashed during a training mission off the coast of northern Nghe An province, with only one of the pilots rescued.
Days later, a military search plane deployed to find the missing pilot lost contact and was later found crashed with all nine people on board dead.
One of the worst accidents in recent years was in July 2014, when 19 people were killed after a Russian-made Mi-171 chopper crashed in the capital Hanoi during a training exercise.
Communist Vietnam has been keen to update its almost exclusively Russian-made military hardware amid tensions with Beijing over disputed territory in the South China Sea.
It is increasingly looking to Western nations to buy military equipment, including the United States after President Barack Obama lifted a Cold War-era ban on arms sales to the country during his visit to Vietnam in May.