In order to study the feasibility of commercial-scale L-lactic acid production by Rhizopus sp. MK-96-1196 using large scale airlift bioreactors (ALBs), a scale-up study from 0.003 m(3) to 5 m(3) ALB was carried out using oxygen transfer rate (OTR) as the scale-up criterion. Enhanced L-lactic acid production was achieved at OTRs higher than 0.28 (g-O-2/l/h) irrespective of the scale of the bioreactor in question: in the range of 0.003 m(3) to 5 m(3), more than 90 g/l L-lactic acid was produced with a yield of approximately 80%, based on the initial glucose concentration. In future research, we plan to design an ALB greater than 3000 m(3) (working volume: 2000 m(3)) for further studies on the production of L-lactic acid in large quantities.