The oxygen transfer and hydrodynamics in viscous media having a yield stress in bubble columns operated under the slug flow regime were investigated to design an optimum bubble column fermentor for culture media having a yield stress.The gas holdup of escapable bubbles was well estimated by the equation of Nicklin et al. (Trans. Inst. Chem. Eng. 40 (1962) 61), which was modified for the viscous liquid having a yield stress by Terasaka and Tsuge (Chem. Eng. Sci. 58 (2003) 513). The volumetric oxygen transfer coefficient k(L)a increased with increasing superficial gas velocity and decreasing column diameter under the present conditions. To predict k(L)a in the non-Newtonian liquids having a yield stress under the operation in slug flow regime, the proposed correlation equation estimated relatively well the experimental k(L)a.To increase oxygen transfer rate, two types of novel bubble columns were compared with the standard bubble column. The partitioned bubble column presented the better performance than those of the other ones. (C) 2003 Elsevier Ltd. All rights reserved.