Stevioside is a no calorie natural sweetener, which is 200-300 times sweeter than sugar. It can be extracted from the leaves of Stevia rebaudiana (Bertoni) and obtained as crystalline solid or odorless powder. Stevioside is approved for use as a supplementary food and food additive in many countries, such as Japan, Korea and United States, including Thailand. Stevioside can be used for diabetic patients and obese persons. The certified reference material of stevioside can be obtained by the purity assessment process, which consists of High Performance Liquid Chromatography (HPLC), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA) and Karl-Fischer (KF) Titration. Quantitative Nuclear Magnetic Resonance Spectrometry (qNMR) can be also used in a quality control in pharmaceutical area.