Two bacteria and three fungi were isolated from the hypogeal stems of Paris polyphylla var. yunnanensis. The bacteria were identified as Bacillus cereus and Pseudomonas alcaligenes, and the fungi were identified as Periconia sp., Pachnocybe albida and Hormomyces paridiphilus. The results on liquid culture of B. cereus, P. alcaligenes and H. paridiphilus indicated that the colloidization and polysaccharide content increasing in hypogeal stems of P. polyphylla var. yunnanensis were due to the extracellular polysaccharide secretion of the parasitical fungus H. paridiphilus.