The optimal geometric design and the mass transfer of ozone for a new gas-induced reactor characterized by the installation of a draft tube and dual pitched-blade turbines were studied. Geometric factors including the impeller diameter, the length and diameter of draft tube, the liquid level, and the impeller speed were investigated to find the optimal gas utilization rate and power consumption for agitation. Furthermore, under the optimal geometric conditions, several variables including the impeller speed, the input gas flow rate, and the liquid level were investigated to reveal the volumetric mass-transfer coefficient of ozone. The optimal geometry was suggested by three empirical equations that correlated successfully the onset impeller speed for gas induction and the power consumption post gas induction with geometrical factors and operational variables. Volumetric mass-transfer coefficients of ozone were 0.8-1.2 min(-1) under optimal geometric and proper operational conditions, which are comparable to the cited values in the literature.