Three men and five women traveling in a car with a Laotian number plate were arrested at a border gate in Quang Nam with 198 kilos of drugs in packets the size of tea bags.
Border guards and police confiscated 15.4 kilos of heroin and 181 kilos of other types of synthetic drugs.
Southeast Asia is a major center for synthetic drugs such as methamphetamine, much of it produced in the border regions of Myanmar.
The mountainous 2,300-kilometer (1,429-mile) Laos-Vietnam border has long been a significant smuggling route.
Vietnam has notoriously tough drug laws, and in January, nine people were sentenced to death and two others to life in prison for their involvement in a trafficking ring from Laos.