Road workers discovered nine RPG grenades at the side of a dirt road, close to the border with Cambodia.
The missiles were found in the Bo Rai district of Trat, with no more than a piece of plastic tape acting as a barrier.
District chief Panuwat Putthakesorn said the grenades may be the remnants from Cambodian factional fighting, and could have lay there for some time.
He further advised that all road workers should be wary in case other weapons or munitions have been discarded in the area.
The area is notorious for landmines. Last year over four hundred mines were destroyed. Cambodia has a major problem with landmines, typically in rural areas in and around the border with Thailand.
There is a legacy of three decades of war, which has taken a severe toll on the country, with over 40,000 amputees as a result from uncharted landmines.