The delegation of 12 priests from the Catholic Priest's Association for Justice (CPAJ) were invited to celebrate Mass in the capital Pyongyang by the Association of Catholics of the North - a government controlled branch of the North Korean Catholic Church.
The invite effectively symbols an invite from the Communist government of North Korea itself, given its hand in the Association of Catholics' affairs.
North Korea has been ranked the worst country in the world for Christian persecution by advocacy charity Open Doors' World Watch List for several years now.
The priests were the first to officially enter the country for seven years, and the Mass celebrated was for the reunification of the two countries.
South Korea authorised their visit, and said in a statement that it could lead to more "in the logic of promoting exchange of a religious type not political."
CPAJ has been campaigning for the reunification of North and South Korea since 1974. The volunteer group of approximately 500 priests is currently working against South Korea's National Security Act.
The law makes a number of practices illegal: Communism, the recognition of North Korea's government as legitimate, or any organisations materials or activities that are "anti-government".
Critics argue the law suppresses free speech and makes South Korea like its northern counterpart, known for its human rights abuses and oppression of religious and political minorities.
Supporters argue the law helps to protect South Korea, and ideologically differentiate it from the North.
