We investigated the effects of dissolved oxygen (DO), influenced by agitation, on the production of lovastatin by 5L fermentations of an isolated high-producing mutant of Aspergillus terreus ATCC 20542. Using measurements of pH and packed cell volume in shaking-flask experiments, a 16hr of the cross-over timing was determined to transfer the most actively growing mycelia in seed over production. Based on results of shaking-flask experiments, we then conducted pilot-scale fermentations in a 5L fermenter at 28 degreesC under 0.5kgw head pressure and 1.0vvm aeration to investigate the effects of programmed DOs on lovastatin production. DO supplies were found to be important to the cells in cultures. The DO levels were critically time-dependent for lovastatin production. While increasing DO levels above 20% of saturation in 24-48hrs, this fermenter operation was found to enhance a 1-day earlier production of lovastatin, in comparison with shaking-flask data. The enhancement was mainly attributed to the formation of compact pellets rather than viscous and filamentous mycelium growth.