The inhibitory effect on inflammatory cytokine production of citrus fruits harvested in Kagoshima prefecture was examined in mouse macrophage cell line. Extracts (with water and ethanol) of the all citrus from Kagoshima had inhibitory effect on production of tumor necrosis factor. In Tankan, the extract of immature peel was more effective than that of mature one. We tried to identify inhibitory component in Tankan. After HPLC fractionation, mass spectrometry was applied for identification of the compound. As a result, it was estimated that the main compound was nobiletin. We detected another more potent inhibitory fraction in the Tankan extract.