The wreckage, without a wing, engine or camera, was recovered when it got caught in his net off Baengnyeong island, a South Korean defence ministry spokesman said.
"Its shape and colour were similar to those of the unmanned aerial vehicles discovered earlier," he said.
In March and April, South Korea retrieved crashed drones equipped with cameras in three different places, including Baengnyeong island and the northern border city of Paju.
Military officials said their memory chips contained pictures of border areas and the capital Seoul, including the presidential palace.
North Korea angrily denied any involvement and accused the South of "fabricating" the evidence.