Crystals of salt of a stereoisomer which is a non-natural type of monatin which are applicable as a sweet taste substance are newly provided. The crystals are stable, have a high degree of sweet taste (high sweetening potency) and are expected for use as a sweetener or an ingredient thereof and also as a component for giving sweet taste to beverage, food, etc.A sweetener using the above-mentioned crystals of the salt which is a novel sweet taste substance and a product such as beverage and food to which sweet taste is given are able to be provided.The stereoisomer salt includes salts of a (2S, 4R) substance, a (2R,4R) substance and a (2R, 4S) substance of monatin and the salt of a (2R,4R) substance of monatin is particularly preferred.
