The present invention provides a process for producing a hydrocarbon oil by performing a Fischer-Tropsch synthesis reaction using a reactor for a Fischer-Tropsch synthesis including a reaction apparatus having a slurry containing catalyst particles and a gaseous phase located above the slurry to obtain a hydrocarbon oil, wherein the Fischer-Tropsch reaction is performed while controlling a temperature of the slurry so that a difference T2−T1 between the average temperature T1 of the slurry and a temperature T2 at the liquid level of the slurry in contact with the gaseous phase is 5 to 30° C.