The Red Purge was an anticommunist movement in occupied Japan from the late 1940s to the early 1950s. Carried out by the Japanese government and private corporations with the aid and encouragement of the Supreme Commander for the Allied Powers (SCAP), the Red Purge saw tens of thousands of alleged members, supporters, or sympathizers of left-wing groups, especially those said to be affiliated with the Japanese Communist Party, removed from their jobs in government, the private sector, universities, and schools. The Red Purge emerged from rising Cold War tensions and the Red Scare after World War II, and was a significant element within a broader "Reverse Course" in Occupation policies. The Red Purge reached a peak following the outbreak of the Korean War in 1950, began to ease after General Douglas MacArthur was replaced as commander of the Occupation by General Matthew Ridgway in 1951, and came to a final conclusion with the end of the Occupation in 1952.

Japan was occupied and administered by the Allies of World War II from the surrender of the Empire of Japan on September 2, 1945, at the war's end until the Treaty of San Francisco took effect on April 28, 1952. The occupation, led by the American military with support from the British Commonwealth and under the supervision of the Far Eastern Commission, involved a total of nearly one million Allied soldiers. The occupation was overseen by the US General Douglas MacArthur, who was appointed Supreme Commander for the Allied Powers by the US President Harry S. Truman; MacArthur was succeeded as supreme commander by General Matthew Ridgway in 1951. Unlike in the occupations of Germany and Austria, the Soviet Union had little to no influence in Japan, declining to participate because it did not want to place Soviet troops under MacArthur's direct command. And unlike Germany, the Japanese government still remained in place throughout the occupation.