This study was designed to evaluate the effect of oxygen transfer from gas phase to liquid phase on pigment production in Monascus ruber NBRC 32318 cultured in a liquid medium composed mainly of rice starch. The cells were cultured in 500-mL baffied Erlenmeyer flasks either by varying the shaking speed from 40 to 200 rpm with a fixed culture volume of 100 mL or by varying the culture volume from 50 to 250 mL with a fixed shaking speed of 120 rpm. Maximum pigment concentration was obtained at a shaking speed of 160 rpm and a culture volume of 100 mL. Cell mass concentration and pigment concentration, evaluated using the volumetric liquid-phase mass transfer coefficient (k(L)a) of oxygen, confirmed that both parameters increased with increase in k(L)a, but reached a plateau when k(L)a was more than 100 h(-1).