A soybean protein beverage having an excellent taste and mouthfeel and high storage stability with preventing formation of a precipitate at a weak acidic region as well as its production process are shown. Said beverage utilizes as its protein source low-phytic acid .beta.-conglycinin obtained by fractionating and purifying .beta.-conglycinin which is a soybean protein fraction and further decomposing and removing phytic acid bound to the resultant .beta.-conglycinin to increase the solubility at a weak acidic region.