Vien finished with a time of 4:37.71. Meanwhile, Shimizu Sakiko of Japan took the silver medal.
With her latest result, Vien set a new Asian record, breaking the old one of 4:41.29 set by China’s Liu Jing in 2002.
However, this is nott Vien’s best timing in this category. At the FINA World Cup in Tokyo last year, she clocked 4:34.50.
Of other Vietnamese representatives, Tran Duy Khoi ranked sixth in the men’s 400m medley with a time of 4:26.40, while Le Nguyen Paul was 13th in the men’s 50m breaststroke with a time of 28.82secs.
Lam Quang Nhat finished 15th in the men’s 200m freestyle with a time of 1:55.16, and Tran Ngoc Thi stood in 10th place in the women’s 200m butterfly event with a time of 2:27.01.
Vien, who won one gold, one silver and one bronze medal at the Military World Games two years ago, will continue her medal hunt in the 200m medley, 400m freestyle, 200m freestyle and 800m freestyle events.
The Asian Swimming Championships will run until April 20.