Abstract In order to investigate whether the mycelia of Poria cocos can ferment and utilize Lentinula edodes stalk substrate and improve its nutritional value and biological activity. P. cocos was cultured on the solid medium using L. edodes stalk as the sole substrate. The kinetic changes of enzyme activities, nutrient composition and antioxidant activity were measured. The results showed that the cellulose exonuclease activity reached 46.14 U/g on the 6th day of the fermentation process, subsequently decreased rapidly to 17.15 U/g, and remained essentially unchanged on the 18th day. The activity of carboxymethyl cellulase and xylanase reached 77.70 U/g and 74.23 U/g, respectively, on the 12th days of fermentation and then gradually decreased. The β-glucosidase activity reached 75.06 U/g on the 18th of the fermentation and then gradually decreased. In comparison with the unfermented L. edodes stalk substrate, total sugar, soluble protein and insoluble dietary fiber of fermented L. edodes stalk substrate showed significant decrease, whereas the contents of reducing sugar, polysaccharidecontents, total phenols, total flavone, amino nitrogen and soluble dietary fiber were increased obviously. The antioxidant capacity of water extracts of fermentation substrate was significantly improved as well. The DPPH radical scavenging rate and the hydroxyl radical scavenging rate increased by 97.75% and 38.15% respectively. The results showed that P. cocos could fermet L. edodes stalk, alter the nutritional components of L. edodes stalk, and that the fermentation substrate exhibited enhanced free radical scavenging ability.