In 1915, during the Bulgarian offensive against Serbia, the division as part of the Second Bulgarian Army took part in the battles near Krivolak, Strumica, Kavadarci and Negotino. The personnel of the division was constantly replenished by soldiers who deserted from the Serbian army to the Bulgarian or to the allied to Bulgaria Austro-Hungarian troops. The following year, 1916, another artillery regiment was added to the 11th Division and it entered the fighting against British units in the Struma Valley. In May 1917 the division was reorganized on the model of the other Bulgarian divisions and its regiments received numbers from 59 to 64. In 1918 two brigades of the division were assigned to the Second Army, and one occupied part of the position in Belasitsa and participated in the Battle of Doiran (1918), in which the First Bulgarian Army repulsed the Anglo-Greek offensive. After the breakthrough at Dobro Pole in September 1918, the division retreated to Gorna Dzhumaya, where it was demobilised. In April 1919, the 11th Division was disbanded. The office of the Division in Sofia became the centre of the restoration of the IMRO and the unofficial headquarters of the organization. Part of the military equipment and weapons of the 11th Division is hidden by the Allied in secret warehouses and was inherited by IMRO.