Saponins are high molecular weight, high polarity compounds which on hydrolysis yield, sugars, uronic acids, and steroidal or pentacyclic triterpenoid aglycones. Both have C-3 sugar linkage and have a common biogenetic origin. Many saponins have an additional sugar at C26 or C28 position. Natural sapogenins differ in their configuration at C-3, C-5, and C-25 positions and in the orientation at C-22 position. Steroidal saponins are C₂₇ sterols in which the side chain of cholesterol has undergone modification to produce a spiroketal as in dioscin. All steroidal saponins have the same configuration at the C-22 spirocenter. Additional stereoisomers at C-25 co occur as mixtures in the plant. They occur in Monocot families such as Dioscoreaceae (Dioscorea sps), Amaryllidaceae (Agave sps), Liliaceae (Yucca and Trillium sps).

Pentacyclic triterpenes (C₃₀) are more widely distributed in nature and occur abundantly in dicots and are based on α-amyrin, β-amyrin, and lupeol. More than 360 different sapogenins representing 750 different glycosides are known. Plant materials contain these saponins in considerable amounts, for example, Liquorice (2–12%), Quillaia (10%), Primula root (5–10%) and Horse chestnut (13%). Oleanolic acid is a common saponin occurring in beet root, thyme, guaiacum sps, and in the free state in olive leaves and clove buds.

Saponins form colloidal solutions in water having a bitter, acrid taste. They occur as milky white amorphous powders and are soluble in water, ethanol, and methanol. They are insoluble in chloroform and benzene. Drugs having saponins are characterized by their sternutatory property and they cause irritation of the mucous membrane. On hydrolysis saponins yield sapogenins, which are readily crystallizable compounds. A large number of carbon atoms in their structure makes them lipophilic and the presence of water soluble sugars gives them a hydrophilic/lipophilic asymmetry resulting in the lowering of surface tension in aqueous solution. This causes foaming in aqueous solutions. Saponins are much more polar than sapogenins because of their glycosidic attachment.