A low viscosity fuel oil has been prepared from black liquor by the following process: (1) thermal treatment of black liquor at 300 - 350 deg C under pressure (20 MPa) in the presence of excess alkali (NaOH), (2) removal of sodium from the black liquor primary oil by acid wash, and (3) catalytic upgrading of the sodium-free black liquor primary oil. The yield of primary oil was about 40 wt% of the initial black liquor organics in the thermal treatment stage. The oil had a sodium content of 7 % (dry matter basis), and only about 1 % of the oil was distillable (< 260 deg C). By washing the oil with dilute acid the sodium content was reduced to 0.02 %. In this case the distillate yield was 11 %. After the catalytic (Ni-Mo/CoMo) two-stage (30 min at 280 deg C and 60 min at 390 deg C) hydro-treatment the oil yield was 88 % and the distillate yield 51 %. The total loss of organics in the wash and upgrading stages was 20 - 25 %.