Saponin isolated from medicinal plants is a naturally occurring bioorganic molecule with high molecular weight and its aglycone (water non-soluble part) nucleus having 27 to 30 carbon atoms besides one or two sugar moieties (water soluble part) containing at least 6 or 12 carbon atoms respectively. The complexity of saponin chemistry maybe considered as a gap for many scientists and researchers to understand the relationship between the chemical structure and its medical or pharmaceutical behavior. Recently, the increase in demand of saponin applications was observed due to various biological, medicinal, and pharmaceutical actions. Therefore, this present review article provides detailed information about the chemistry of saponin, especially triterpenoid saponin. Classifications, chemical structure, the possible traditional isolation ways, qualitative, and quantitative determination of saponins were included exclusively. Examples of mono and bidesmosidic structure of oleanolic acid and hederagenin also outlined. Structural differences between triterpenoid, steroid, and alkaloid glycosides were summarized according to their atoms, rings, and functional groups.