The ozonation process has been widely used for drinking water disinfection around the world. Recently, the pressurizedozone contactor, in which the side stream typed ozone injection method is installed, has been applied to water treatmentsystem. In this study, numerical calculations were conducted to compare prototype and screw-type ozone contactors basedon hydraulic effectiveness in more details. The prototype ozone contactor was already installed and operated in domestic watertreatment plant, and the screw-type is the suggested one for improving ozone contact efficiency installing the screw plate tothe prototype. Screw turn numbers of screw plate were changed as 3, 5, 7 and 9, respectively for numerical simulation. TheCT(concentration of disinfectant in mg/L times time in minutes) value was considered as one of the options for evaluating disinfectionability. From the results, it could be concluded that the performance of the screw-type is higher than that of the protypecontactor by controlling the variable T as the tracer time. Also, Morill index of the screw-type(turn numbers = 5 ) appeared to belower than the other.