An event to mark the occasion was held on Monday in front of a monument commemorating the seawall's completion.
World's Longest Seawall - Saemangeum Dike Picture
According to Guinness World Records, the dike is 1.4 km longer than the previous record holder, the Zuiderzee Works in the Netherlands.
Some 3.9 million people have visited the site along the west coast of Korea since it was finished in April, the Korea Rural Community & Agricultural Corporation said.