Central composite rotatable design (CCRD) was applied for analyzing and optimizing the effects of impeller rotational speed, gas flow rate, probe location, and tracer injection point on the gas-liquid two-phase mixing time in an agitated vessel with a dual six-blade Rushton turbine. Knowledge of the effects of independent factors on the mixing time is necessary in order to optimize the mixing process. The mathematical relationship between mixing time and four significant independent variables can be approximated by a nonlinear polynomial model. The obtained results demonstrate that CCRD could efficiently be applied for modeling mixing time. It requires fewer experimental runs and provides sufficient information as compared to a factorial design.