The South Korean ship and its 10 crew returned home after being questioned for several hours by officials in the North.
The two Koreas remain divided after the 1950-53 Korean War ended in an armistice, but with no formal peace treaty.
In the years since, South Korea achieved rapid economic growth through exports and manufacturing, with per capita income soaring far above levels in the North.
Relations between the North and South briefly improved after a 2000 summit between their leaders, but despite increased trade ties military tensions between the two sides remain high.