Slags from metallurgical industry are cost efficient alternatives for acidic zeolites in catalytic fast pyrolysis. A slag from steel industry was studied for catalytic fast pyrolysis of pine sawdust. The desulfurization slag from a blast furnace steel mill was modified to improve its catalytic properties by using alkaline pretreatments and hydrothermal syntheses. As a result, specific surface area of the material could be increased. Modified desulfurization slags were tested using analytical pyrolysis and bench scale bubbling fluidized bed pyrolyser. Results of analytical pyrolysis indicate that slags are able to modify product distribution. Based on these results, the best modified slag was chosen for bench scale pyrolysis tests. In the bench scale run, the use of modified slag led to oxygenated bio oil compared to fast pyrolysis with sand. However, bio oil yield decreased simultaneously as typically in catalytic fast pyrolysis.