The Spanish Flu was one of the disasters in the history of Iran, especially Southern Iran, which led to the death of a significant number of people in Iran. It started on October 29, 1917, and lasted till 1920 – a disaster that we can claim changed the history. In one of the First World War battlefields in southern Iran in 1918, there was nothing left until the end of World War I and when the battle between Iranian warriors (especially people of Dashtestan and Tangestan in Bushehr, Arabs, and people of Bakhtiari in Khuzestan and people of Kazerun and Qashqai in Fars) and British forces had reached its peak. As each second encouraged the triumph for the Iranians, a flu outbreak among Iranian warriors led to many deaths and, as a result, military withdrawal. The flu outbreak in Kazerun, Firoozabad, Farshband, Abadeh, and even in Shiraz changed the end of the war. In this article, we attempt to discuss the role of the Spanish flu outbreak at the end of one of the forefronts of World War I.