Accelerated deactivation of ruthenium-promoted alumina-supported alkalized cobalt (K-Ru-Co/γ-Al 2 O 3 ) Fischer-Tropsch (FT) synthesis catalyst along the catalytic bed over 120 h of time-on-stream (TOS) was investigated. Catalytic bed was divided into three parts and structural changes of the spent catalysts collected from each catalytic bed after FT synthesis were studied using different techniques. Rapid deactivation was observed during the reaction due to high reaction temperature and low feed flow rates. The physico-chemical properties of the catalyst charged in the Bed #1 of the reactor did not change significantly. Interaction of cobalt with alumina and the formation of CoAl 2 O 4 increased along the catalytic bed. Reducibility percentage decreased by 4.5%, 7.5% and 12.9% for the catalysts in the Beds #1, #2 and #3, respectively. Dispersion decreased by 8.8%, 14.4% and 26.6% for the catalysts in the Beds #1, #2 and #3, respectively. Particle diameter increased by 0.6%, 2.4% and 10.4% for the catalysts in the Beds #1, #2 and #3, respectively, suggesting higher rate of sintering at the last catalytic bed. The amount of coke at the last catalytic bed was significantly higher than those of Beds #1 and #2. Accelerated deactivation of ruthenium-promoted alumina-supported alkalized cobalt (K-Ru-Co / γ-Al 2 O 3) Fischer-Tropsch (FT) synthesis catalyst along the catalytic bed over 120 h of time-on-stream investigated. Catalytic bed was divided into three parts and structural changes of the spent catalysts were from each catalytic bed after FT synthesis were studied using different techniques. Rapid physique was observed during the reaction due to high reaction temperature and low feed flow rates. -chemical properties of the catalyst charged in the Bed # 1 of the reactor did not change significantly. Interaction of cobalt with alumina and the formation of CoAl 2 O 4 increased along the catalytic bed. Reducibility percentage decreased by 4.5%, 7.5% and 12.9 % for the catalysts in the Beds # 1, # 2 and # 3, respectively. Dispersion decreased by 8.8%, 14.4% and 26.6% for the catalysts in the Beds # 1, # 2 and # 3, respectively. Particle diameter increased by 0.6%, 2.4% and 10.4% for the catalysts in the Beds # 1, # 2 and # 3, respectively, suggesting higher rate of sintering at the last catalytic bed. The amount of coke at the last catalytic bed was significantly higher than those of Beds # 1 and # 2.