The effects of two types of Welsh onion, green-leafy and white-sheath types, on hyperlipidemia in rats fed on diets high in fat and sucrose were studied. A significant lowering effect on cholesterol in the plasma and on total lipids, triacylglycerol, and cholesterol in the liver was observed in rats fed on the green, but not white, Welsh onion. These Welsh onions had no significant effect on the hepatic enzyme activities responsible for fatty acid synthesis and degradation. The results suggest that the green Welsh onion might be effective in attenuating hyperlipidemia in a manner other than affecting fatty acid metabolism in the liver. Kaempferol seemed to be one of the components in green Welsh onion acting to lower lipid deposition.