This study was conducted to investigate the effects of a buckwheat protein product (BWP) on plasma cholesterol, gallbladder bile composition and fecal steroid excretion in hamsters fed diets with 5 g/kg cholesterol. Diets also contained 200 g/kg of casein, soy protein isolate (SPI) or BWP as protein sources. After 2 wk, plasma and liver concentrations of cholesterol in the hamsters fed BWP were significantly lower than those in the hamsters fed casein and SPI. The molar proportion of cholesterol in gallbladder bile was significantly lower in the BWP group than in the other groups, whereas that of bile acids was slightly higher in the BWP group (P </= 0.05), resulting in the lowest lithogenic index in the BWP group. None of the hamsters fed BWP had gallstones, whereas they were present in some of the hamsters fed other proteins. Compared with casein intake, BWP intake resulted in significantly higher ratios of cholic acid to chenodeoxycholic acid and of cholic acid to lithocholic acid in the gallbladder bile. The excretions of fecal neutral and acidic steroids were markedly higher in the BWP group compared with the other groups (P </= 0.05). SPI intake also significantly lowered cholesterol level in gallbladder bile and caused higher fecal bile acids compared with casein intake, but the effects were significantly less than those of BWP (P </= 0.05). The results suggest that BWP suppresses gallstone formation and cholesterol level more strongly than SPI by enhancing bile acid synthesis and fecal excretion of both neutral and acidic steroids.