Giang A Lanh, 34, and Ly Thi Mai, 32, in Vietnam's northern province of Dien Bien, are facing charges for "illegally transporting narcotic substances."
They were detained while on their way to transport around 11 kg of heroin from Dien Bien to Lao Cai Province, which borders China.
The two told police that they were hired by a Chinese person, whose identity has not been found, to travel to Laos and bring the drugs to Lao Cai. They were paid VND320 million ($14,000).
After returning to Dien Bien, they hid the drug on a hill before being instructed to send it to China. On Wednesday, Mai put the drug into a bag of clothes and traveled to Lao Cai on a passenger bus from Dien Bien.
Lanh followed her on a motorbike.
The two met in Lao Cai in the first hours of Thursday and as they were preparing to hand over the drug to a third person, were caught by border guards.
Police said they had kept the duo under surveillance for around a month.
Vietnam has in recent years become a key trafficking hub for narcotics around the Golden Triangle, an intersection of China, Laos, Thailand, and Myanmar and the world's second-largest drug-producing region, after the Golden Crescent in South Asia.
It also has some of the world's toughest drug laws. Those convicted of possessing or smuggling more than 600 grams of heroin or more than 2.5 kilograms of methamphetamine face the death penalty.