Methods of preparing highly purified steviol glycosides, particularly rebaudiosides A, D and M are described. The methods include utilizing recombinant microorganisms for converting various staring compositions to target steviol glycosides. In addition, novel steviol glycosides reb D2 and reb M2 are disclosed, as are methods of preparing the same. The highly purified rebaudiosides are useful as non-caloric sweetener in edible and chewable compositions such as any beverages, confectioneries, bakery products, cookies, and chewing gums.