The data was compiled by the Australian Department of Home Affairs from July last year to April this year for visas granted to people studying in high school, university, vocational courses, and short-term English courses.
This is the only the second time since 2005 that the visa approval rate for Vietnamese students has dropped below 80%; it typically ranges between 85% and 99.7%.
The most rejections were for vocational and English language students, with the rates being 46.8% and 48.4% as against less than 40% previously.
For undergraduate and postgraduate levels, the approval rate were 90-100%.
The decrease in visas granted primarily for short-term courses (6-24 months) comes as Australia tightens immigration, rolling out a number of new policies since last year.
Last week the Home Affairs Department announced that from next month it would stop converting tourist visas to student visas.
Last month Australia increased the financial proof requirement for international students by 20% to AUD$29,700 (US$19,800).
In March the English requirement for international students was raised to 6.0-6.5 IELTS, 0.5 points higher than before, and a part-time work limit was brought in.
In February the country reduced international students’ stay to a maximum of four years from the earlier six.
Data from the Home Affairs Department shows a drop of nearly 30% year-on-year in student visa issuances in the first four months of 2024.
A total of 74,421 were granted.
But Professor Tran Thi Ly, an international education expert at Deakin University, said the stricter policies notwithstanding, many schools still target Vietnam since it is a reliable market with diligent, high-achieving students.
Australia is one of the most popular study destinations in the world.
International education is one of Australia's largest export industries and was worth AUD36.4 billion ($24.3 billion) last year.
As of March this year there were over 740,000 foreign students, with Vietnamese accounting for 5%.