The 1.8-meter-long MK-83 bomb was found by local man Nguyen Khac Dung while going to his field to work in Loc Ha District. It had been unearthed by the recent floods and erosion, local authorities said.
The site where it was found has been cordoned off, and the military took it to a shooting range in Thach Ha District to defuse it, they said.
Several districts in the province, including Loc Ha, were sites where thousands of bombs were dropped during the war.
While the war ended more than 40 years ago, around 800,000 tons of unexploded ordnance remain scattered across the country, according to government data.
Ha Tinh and several other central provinces suffered from heavy rains this month, and the resultant flooding and landslips killed at least 130 people and damaged roads and buildings.