We evaluated the anti-tumor activity of fermented grain extracts using a mouse tumor model. An experimental diet containing materials from fermented rice germ, wheat germ, hulled rice, soybean and seaweed (fermented materials, FM) was fed to 4-week-old female C57BL6 mice for 14 days prior to and 21 days following the subcutaneous implantation of B16 melanoma (5×10 ⁵ cells/mouse). FM retarded tumor growth and increased the duration of host survival. We further examined the anti-tumor activity of FM using the B16 metastasis model. An experimental diet containing FM was fed to C57BL6 mice for 14 days prior to and 21 days following B16 tail vein administration (5×10⁴ cells/mouse). The decrease in observed metastasis in the lungs of mice treated with FM was also significant. In order to identify this anti-tumor activity of FM, NK-activity in the FM fed mice was evaluated. However, the values were comparable to the control mice. These results suggest that the fermented grain extracts induce anti tumor activity in vivo, although the mechanism of this activity is not yet clear.