Danang's airport is one of three known dioxin hot spots in Vietnam.
The United States has given about $60 million for environmental restoration and social services in Vietnam since 2007, but this is its first direct involvement in dioxin cleanup.
The project begins as Vietnam and the United States forge closer ties to boost trade and counter China's rising influence in the region.
Although the countries' economic and military ties are blossoming, progress on dioxin has been slow. Washington still disputes an assertion by Hanoi that up to four million Vietnamese were affected by toxic chemicals sprayed by U.S. planes during the war. The United States argues that the actual number is far lower and that other environmental factors are to blame for health problems.
That position irks Vietnamese, who say the United States maintains a double standard in acknowledging the consequences of Agent Orange.
The United States has given billions of dollars in disability payments to U.S. service personnel who developed illnesses associated with dioxin during the war.
Vietnam's Ministry of Defense and the United States plan to excavate 2.5 million cubic feet of soil from the airport and heat it to a high temperature in storage tanks until the dioxin is removed. The project is expected to be completed in four years.