Biomass and its glucosamine content were measured for Monascus ruber after its cultivation on solid media containing different amounts of rice starch and protein. The protein was supplied as either yeast extract or peptone. The ratios of carbohydrate weight and protein weight (C/P ratio) in the media in this study were 2.2, 2.7, 20, 29, 34, and 60. Biomass production increased when the C/P ratio increased. The results show a linear relationship between the glucosamine content in biomass of M. ruber and the C/P ratio of media. We have successfully used this linear relationship to predict the glucosamine content in the biomass of M. ruber on rice flour medium. The error in this prediction method is not more than 15%.