The e!ect of liquid #ow condition on the growth of red beet hairy roots was investigated with a single-column reactor (SCR) at super"cial velocities of medium ranging from 2 to 28 m/h, and the optimal growth was obtained when the super"cial velocity was kept at 15 m/h in the culture for 190 h. The increase in medium #ow caused the enhancement of elongation rate and decline of viability at tip meristems of the hairy roots, resulting from the enhancement of both the dissolved oxygen (DO) concentration and shear stress at hairy root surfaces, respectively. Speci"c cross-sectional area of bioreactor was de"ned as an evaluation parameter and a variation in the speci"c cross-sectional area was found to a!ect DO concentration at hairy root surfaces. Based on evaluated value of the speci"c cross-sectional area, a radial #ow reactor (RFR) was constructed to perform the high-density culture of red beet hairy roots. Under the conditions of void fraction of hairy roots of 0.3}0.7, super"cial velocity of 15 m/h and speci"c cross-sectional area of 40 m, it was estimated that the DO concentration at hairy root surfaces increased with increasing cell mass concentration. During the culture in the RFR at super"cial velocity of 15 m/h, the serious declination of DO concentration in bulk liquid did not occur owing to improvement of oxygen supply. The "nal density of hairy roots in a growth unit of the RFR reached 51 kg dry weight/m at culture time of 280 h.