It came in response to the firm being ordered to pay $289m (£226m) to a school groundsman who claims his use of its Roundup weedkiller contributed to his terminal cancer.
“The verdict serves as a legal precedent which refutes previous claims that the herbicides made by Monsanto and other chemical corporations in the US and provided for the US army in the war are harmless,” a spokesman for Vietnam’s foreign ministry, Nguyen Phuong Tra said.
He told state media: “Vietnam has suffered tremendous consequences from the war, especially with regard to the lasting and devastating effects of toxic chemicals, including Agent Orange.”
Agent Orange was a chemical herbicide and defoliant used by the US military to deprive Viet Cong guerilla fighters of food and concealment.
Between 1961 and 1971, the US military sprayed around 12 million gallons of the chemical substance on over 30,000 miles of southern Vietnam.
Dioxin, a highly toxic element of Agent Orange, has been linked to major health problems such as birth defects, cancers other deadly diseases.
Millions still suffer to this day, as deformities are passed down to the offspring of exposed victims including Vietnamese and American forces.
Monsanto has argued: “The government set the specifications for making Agent Orange and determined when, where and how it was used. Agent Orange was only produced for, and used by, the government.”
In a post on its website, the company notes it was one of nine government contractors who manufactured the chemical.
Monsanto was founded in St Louis, Missouri, in 1901. In June, it was acquired by Bayer AG.