Sorghum, Sorghum bicolor (L.) Moench, is the fifth most important cereal crop in the world. In this study, we identified the IgE production-suppressing activity of white sorghum bran extracts. White sorghum is one of the genotypes of sorghum. White sorghum bran extracts in 10 mM sodium phosphate buffer (pH 7.4) suppressed IgE production in human myeloma cell line U266. The extracts suppressed IgE production by decreasing mRNA transcription level of IgE, but they did not affect IgA or IgG production of mice splenocytes in vitro. Heat treatment and trypsin digestion did not affect IgE production-suppressing activity. The white sorghum bran extracts were fractionated by ultrafiltration, and the molecular weight of the active substance was estimated to be less than 1,000.