Monacolin K, an inhibitor for cholesterol synthesis, is the secondary metabolite of Monascus species. The formation of the secondary metabolites of the Monascus species is affected by cultivation environment and method. This research uses sweet potato (Ipomoea batatas), potato (Solanum tuberosum), casava (Manihot esculenta), and dioscorea (Dioscorea batatas) as the substrates and discusses the best substrate to produce monacolin K. The results show that Monascus purpureus NTU 301, with dioscorea as the substrate, can produce monacolin K at 2,584 mg kg(-1)supercript stop, which is 5.37 times to that resulted when rice is used as the substrate. In addition, more amount of yellow pigment can be found in Monascus-fermented dioscorea than in Monascus-fermented rice. The certain composition of yellow pigment is identified as monascin, which has been shown as an antiinflammation agent exhibiting potent inhibitory effects on 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced inflammation in mice in previous studies. Therefore, dioscorea is concluded to be the best substrate for Monascus species to produce the cholesterol-lowering agent-monacolin K and antiinflammation agent-monascin.