Nguyen Van Thuong, 31, was found carrying two K59 pistols when he crossed the border through My Quy Tay in Duc Hue District Friday afternoon.
Long An border guards, in cooperation with customs officials, checked Thuong's luggage and found the pistols, along with 25 bullets. He was then detained for further investigation.
Long An has a border spanning over 134 kilometers, next to Cambodia's Svay Rieng and Prey Veng borders. Since the beginning of this year, authorities have detained over 30 people for illegally crossing the border.
Vietnam does not allow gun ownership among residents.