The present invention provides an improving agent for cooked rice, which can provide a frozen cooked rice having similar quality not only in mouthfeel and appearance but also in taste and smell to the ordinary cooked rice when the frozen cooked rice is thawed and heated by microwave heating. The improving agent for cooked rice is prepared by pulverizing a nonglutinous rice to obtain a rice powder which retains the cellular structure of each cell in the nonglutinous rice, which cell structure retains the cell wall,； mixing the obtained rice powder with water to a rice powder content of 1 to 10 wt% in water； and heating the obtained mixture such that a degree of gelatinization thereof becomes not less than 85%, preferably not less than 90%. The rice powder having a mesh size of between 100 and 300 mesh is used as the above-mentioned rice powder, and the viscosity of the improving agent is adjusted to not more than 1/3 of the maximum value of the viscosity which is observed when the rice powder-water mixture is heated continuously measuring the viscosity of the mixture with time.
