The Catholic Church was destroyed and greatly damaged during the three-year Korean War. Because foreign missionaries did not take refuge to protect their parishes and parishioners, they were captured or killed by the North Korean army. Because of this, the Catholic Church became increasingly anti-communist during the Korean War and even recognized the Korean War as a holy war or crusade. However, existing studies that analyze the relationship between the Cold War and religion from a macro perspective are limited by their inability to capture the "voices" of the specific people who made up the Christian church and encountered communism. The writings of the missionaries who suffered, however, make it difficult to simplify the Korean War as a holy war against the devil. The Missionary Society of St. Columban kept records of investigative reports on missionaries who were abducted or killed during the war, efforts to negotiate an armistice and release prisoners of war, and reports on the status of wartime missions. Until now, studies on the activities and documents of missionaries during the Korean War have been organized by religious orders and foreign missions, including introductions to the activities and documents of Maryknoll, Benedictine, and Golumban missions, but few have comprehensively summarized them. This article examined missionaries' memoirs written after their release from the camps following their death marches and Columban documents that show missionary activities in the midst of war to understand how missionaries fulfilled their mission in attitudes and practices that intensified hatred, hostility, and ideological opposition. In doing so, it explored the attitudes and practices of missionaries in the face of intensifying hatred, hostility, and ideological opposition, and the efforts they made to rebuild the church in the South Korea during the war. The diaries of the missionaries who survived the death march described martyrdom, but also showed Christian faith and reflection unrelated to anti-communist or Cold War ideology. The missionaries' testimonies of their kidnapping include a spirit of martyrdom and prayers for forgiveness and repentance. In a time of war, when hatred, hostility, and ideological confrontation were bound to intensify, the missionaries carried out their mission and faith without being bound by ideology. The martyrdom of the missionaries and the return of the abductees in 1953 were widely publicized not only in their respective religious orders but also in their home countries of the United States, France, Germany, the United Kingdom, Ireland, and Australia. Monastic orders and Catholics in their home countries actively supported the returning missionaries when they re-entered Korea after the armistice in July 1953 and organized missionary marches. The sufferings and martyrdom of the missionaries provided the basis and impetus for the active mission and relief work in and after wartime South Korea.