Abstract: Stevioside is the most abundant in steviol glycosides, but tasted bitter.In this study, Gibberella fujikuroi was used as original strain.A mutant strain MS05 was obtained after treated with ultraviolet (UV) and 5-bromouracil (5-BU) , which could transform stevioside into rebaudioside A, a kind of steviol glycosides tasted more sweet and less bitter.After fermentation RA content increased 22.98% than original strain, increased 39.29% than before fermentation.