Stevia rebaudiana (Eupatoriae, Compositae), a wild herb of Paraguay (local name: Kaa he-e) has been known to contain the sweet diterpene-gucoside named stevioside (1) (yield: 5∼10% aglycone: steviol (2)) in its leaves. Since withdrawal of cyclamate and saccharin from the consumer`s market because of their toxicities, leaves of this plant have attracted special attention as the new source of the natural sweenteners and cultivation of the plant has been elaborated in Japan as well as other East-Asian countries. The extract or a glycoside-fraction of this plant is now used commercially as a food additive in Japan. On the search of other sweet glycosides, we isolated several new sweet steviol-glycosides from the leaves, designating them as rebaudiosides-A(3), -C(4), -D(5), and -E(6) and the structures of these glycosides were elucidated as shown in the Chart by means of the modern procedures such ^(13)C NMR, field desorption mass spectrometry, and a variety of glycosidases. Prof. Mitsuhashi`s group, Hokkaido University also isolated two glycosides, named dulcosides-A (7) and -B, latter of which was identical with our rebaudioside-C. It was found, 3, 5, and 6 taste sweeter and more pleasant rather than 1. We succeeded to convert 1 into 3, 5, and 6 in a fairly good yield by combination of chemical and enzymic methods. By chemical and enzymic procedure (using the potential glucosyltransferase), we prepared a variety of glycosides of this type (more than 20 compounds), which along with the naturally occurring glycosides of ent-kaurenoic acid derivatives, allowed study on the structuresweetness relationship. It was disclosed that the 19-C-0-glycosyl and 13-0-glycosyl functions as well as the 16-17 double bond play the essential role in revelation of sweentness of the glycosides of this type. It was also demonstrated that 3 and 5 having a branched sugar moiety exhibit the sweetest and relatively most delicious taste among the glycosides examined in our study. Besides the sweet diterpene glycosides, we isolated three labdane-type diterpenes from leaves of this plant jhanol, austroinulin and its 6-0-acetyl derivative, the former two of which were already isolated from other plants of Eupatoriae. Separation and quantitative analysis of the sweetglycosides in the leaves and chemical studies on the constituents of other Stevia spp., S. serrata, S. ovata, and S. paniculata all of which contain no sweet glycosides, will be also presented. (도표)