BACKGROUND: beta-Estradiol is an important hormone for the treatment of breast cancer and osteoporosis. beta-Estradiol can be produced via Saccharomyces cerevisiae mediated reduction of estrone. However, substrate inhibition and low production yield have been observed in the batch cell culture. RESULTS: An innovative continuous cell culture with dual stirred tanks in series was designed to solve the above problems. The growth medium was fed continuously to the incubation tank where the cells were incubated aerobically; the viable cells were then supplied continuously to the reaction tank in which the yeast-mediated anaerobic reduction of estrone was performed with continuous feed of the substrate medium and continuous withdawal of the reaction cell culture. Thus, an increase in cell productivity from about 3-fold to 7-fold was obtained when compared with the batch cell culture. The beta-estradiol yield was improved to 64.8% on the second reaction day, accompanied by an accumulation of 12.9mg beta-estradiol on the third reaction day. The yield was about 10% more and the accumulated recovery of beta-estradiol was 4.3-fold better than with the batch cell culture. The diastereomeric excess value (%de) of beta-estradiol was more than 99%. CONCLUSION: A high product yield with excellent stereo-selectivity was achieved in a short reaction period with the developed continuous cell culture and the dual stirred tank. (C) 2010 Society of Chemical Industry