There is disclosed an aqueous dispersed solution as a standard solution for determining lipid levels, having a dispersion form and a particle size, which are similar to those of serum lipids. A lipid-dispersed solution is obtained by evaporating an organic solvent from a mixture prepared by adding cholesterol, a phospholipid, a bile acid or bile acid salt, and a neutral lipid and/or a cholesterol ester in the organic solvent, swelling the resultant thin-film like mixture with water or buffer heated at a temperature higher than a phase transition temperature of the lecithin, and then dispersing the solution by a physical shear force. There can be easily obtained a solution having a cholesterol concentration of about less than 1,000 mg/dl, which is extremely stable and can be stored for a long period of time.