Oxygen scarcity may significantly affect the process performance since it has low aqueous solubility and high demand by chemical and biological processes. The oxygen mass transfer is therefore necessary to enhance. This work aimed to develop the gas-liquid reactor, named Modified Airlift Reactor (MALR) for improving the oxygen transfer efficiency in terms of internal configurations and aeration parameters by equipping a vertical baffle for creating liquid circulation phenomena, and installing slanted baffles in the reactor riser to extend air-bubbles retention time and to improve their distributions. Since extremum conditions of the investigated factors may inefficient, optimum levels are required to identify. 2(k)factorial and response surface design of Design of Experiment (DOE) methodology were applied to optimize these complex variables in terms of overall liquid mass transfer coefficient (K(L)a) of clean water. As a result, the main effective factors of MALR with their optimum value are amount of baffles (N-b similar to 3 baffles), baffle angle (alpha similar to 50 degrees), position of base area (Y-r similar to 10 cm), open space on baffle (A(s)similar to 90 cm(2)), and gas flow (Qg). Increasing Qg resulted betterK(L)afor the studied ranges (2-18 LPM). At the optimum condition, the improvement of MALR in terms ofK(L)acoefficient was increased up to 97% and 28% compared to the regular bubble column and airlift reactor, respectively, at a certain gas flow without any extra energy. The correlation models ofK(L)acoefficient with significant variables and power consumption were constructed for future estimation purposes.