Article 809 of the Korean Civil Code (Korean: 809) was the codification of a traditional rule prohibiting marriage between men and women who have the same surname and ancestral home (bon-gwan). On 16 July 1997, the Constitutional Court of Korea ruled the article unconstitutional. The National Assembly of South Korea passed an amendment to the Article in March 2002, which came into force on 31 March 2005, and prohibited marriage only between men and women who are closely related.

What's the best answer to this question: can you marry someone with the same last name in korea?
yes