Abstract: The changes of the vitality of Armillaria mellea of infecting corm of Gastrodia elata were observed by appling the live body staining method of acridine orange and by means of fluorescence microscopy. The green fluorescence of vitality was emitted by the first infected hyphae, the yellow one by the decrepit hyphae; but the orange to red fluorescence with the lost vitality were emitted by the fragmentary hyphae and clump form bodies. The large cells containing rich, RNA and protein had been confirmed by the method of the induced fluorescence which the acridine orange and by the method at pH 2.2 which the fast-green staining. The acid-phosphatase was mainly distributed within the cortical cells filled with the infected hyphae. There were few such deposits in the socalled large cells except their walls. The activity of the esterase was shown in the cortical cells filled with the infected hyphae. It were also shown in the clump form bodies and the collapsed nuclei of the large cells. The activities of adenosine triphosphatase (ATPase), peroxidase and polyphenol oxidase was notably shown in the cortical cells filled with the infected hyphae and the large cells.