The conversion of glucose in mirin (an alcoholic seasoning) to fructose using immobilized glucose isomerase (IGI) was studied in order to produce sweetened mirin without chill haze. The initial conversion velocity (Cm/tm) with IGI was affected by temperature, pH, and ethanol concentration. This reaction was first order, for which the temperature coefficient (Q10) over the range 20–55°C was 2.0. The value of Cm/tm was a maximum at pH 8.0, and decreased with an increase in ethanol. Conversions carried out in a continuous column reaction system had Cm/tm values 36 times higher than that in a batch system. Mirin treated with IGI did not form chill haze.