The vessel, AG-20292, was stopped at 2.43 am about eight nautical miles northeast of Mui Nai by Coast Guard and Border Guard forces during a joint patrol.
The boat was captained by Van Thanh Nhon, 54, from An Giang, and had one other crew member on board.
During the inspection, the crew were unable to provide invoices or other documents showing the lawful origin of the sugar. The crew member also failed to produce the professional qualifications required under regulations.
Authorities made an initial record of the case and escorted the vessel to the port of Ha Tien International Border Gate Border Guard Station at around 5 am for temporary detention.
The case is under further investigation.