Minor ginsenosides, low content in ginseng, have higher pharmacological activities. To obtain minor ginsenosides, the biotransformation of American ginseng PPD-ginsenoside was studied using special ginsenosidase type-I from Aspegillus niger g.848. The methods of DEAE-cellulose and PAGE were used in enzyme purification, TLC and HPLC were used in enzyme hydrolysis and kinetics; crude enzyme was used in minor ginsenoside preparation from PPD-ginsenoside; the products were separated with silica-gel-column, and recognised by HPLC and NMR.