We have shown previously that Japanese radish (Raphanus sativus) sprouts (JRS) improve blood glucose levels in diabetic rats. In this study, we investigated the components in JRS that caused this hypoglycemic effect, by examining the effects of water-soluble (WSE) and fat-soluble (FSE) extracts of JRS on diabetes markers in normal (NM) and streptozotocin (STZ)-induced diabetic (DM) rats. The NM and DM rats were divided into a control group and 2 test groups (WSE (2.2%) or FSE (0.2%)), with the rats (n=6/group) then being maintained for 3 wk on either a control diet or one of the test diets; this was followed by the measurement of serum concentrations of glucose, insulin, glycoalbumin, fructosamine, ketone bodies, and lipids (cholesterol and triglyceride) and liver concentrations of lipids (total lipid, total cholesterol, and triglyceride). The FSE suppressed insulin secretion and improved lipid metabolism in the NM rats. The effect of WSE was different from that of the FSE as it decreased blood glucose levels without increasing insulin secretion and also lowered glycoalbumin and fructosamine levels in the DM rats. Therefore, the WSE have potential as functional food components with the hypoglycemic effect.