Disclosed is a method for producing tertiary butyl alcohol through hydration reaction of isobutylene and water in the presence of a cation exchange resin by using a reactor having at least two reactor vessels provided in series. The method is characterized in that a fluid in a reactor vessel at the most downstream side forms a two-liquid phase and the reaction temperature of the reactor vessel is kept at 70° C. or lower, and a fluid in at least one reactor vessel other than the one at the most downstream side forms a homogeneous phase.