An effective experimental design was used to determine the optimal ingredients and compositions in submerged cultures of Aspergillus terreus for lovastatin production. Through medium optimization, lovastatin production of a 7-day fermentation process was maximized at (g/l): glucose (20.0), lactose (89.5), glycerol (30.2), peptone (6.0), soybean meal (4.2), and corn steep liquor (10.0), respectively. This optimized medium resulted in a 4.18-fold increase in lovastatin titres (i.e., 1.05 g/l), as compared with that using basal medium. The lovastatin-producing phase was further increased if adding 0.1 g/l D,L-methionine at 72 hr, which enhanced lovastatin production by 14-17%. However, no benefit was provided to stimulate lovastatin production in the strain when this dosage was added in medium initially or during late idiophase. An adverse effect was also found when the L-methionine was applied.