A source from the education ministry said all four Vietnamese students sent to the contest in Thailand have earned high scores.
Dinh Quang Hieu, a 12th-grader from Hanoi, scored 92 out of 100 which put him in the top 10 of nearly 300 contestants. The other gold winners ranked 20 and 21.
Hieu was also one of two gold medal winners in the Vietnamese team last year.
Although the final ranking this year has not been announced, the Vietnamese team is claiming the second spot, together with China. American students dominate the contest with four gold medals, according to the ministry.
Vietnamese students have fared well in chemistry this year.
At the national high school graduation exam last month, 1,520 chemistry papers scored the perfect 10 out of 10, the highest number out of all nine subjects. English came second with 996 faultless papers.