Abstract: Twenty-two phytopathogenic fungi were screened with regard to their ability to produce minor ginsenoside compound K (C-K) . Six fungi were detected to be able to convert major protopanaxadiol type saponins to ginsenoside C-K in the all tested strains, and the No. 1. 91 fungal strain which showed the most efficient biotransformation was morphologically identified as Oospora Wallr. The biotransformation pathways of ginsenoside Rb1 and Rb2 by No. 1. 91 fungal strain were:Rb1→Rd→F2→C-K, Rb2→C-O→C-Y. The following optimum conditions for transforming C-K by No. 1. 91 fungal strain were determined:the time of substrate addition, 12h, pH5. 0 ～ 6. 0 and temperature 45℃. This study laid a certain foundation of the industrial preparation of minor ginsenoside C-K.