PURPOSE: To produce a whey sour base not forming precipitate even by extremely long-period preservation, having a good flavor, by subjecting a prepared solution comprising whey protein as a main component to lactic acid fermentation, blending the solution with a glucide and an acid and homogenizing the blend.

CONSTITUTION: One of a mixture of whey, concentrated whey, whey powder, whey protein condensate, etc., is processed to give a solution having 6W16% solid content concentration at ≥6.7pH, preferably 6.8W7.2pH and the solution is sterilized under heating inoculated with lactic acid bacteria and fermented by a conventional procedure. Then, the prepared fermented solution having 0.3W1.8% final lactic acid concentration at about 4W4.5pH is blended with 20W50wt% glucide such as sugar, sorbitol, etc., and an edible acid such as lactic acid, citric acid, etc., in an enough amount to adjust the solution to 2.3W3.5pH, sterilized and homogenized.