For the fermentation of Cordyceps militaris with germinated soybean, Lactobacillus plantarum KCB001, which showed good growth on the medium containing the mushroom and soybean, was isolated from kimchi and selected as a starter for the fermentation. The optimum conditions for the solid-phase fermentation of C. militaris with germinated soybean were a ratio of 4:1, the addition of water and starter culture at the final concentrations of 40%(v/v) and 20%(v/w), respectively, and fermentation at 37°C for 72 h. Total polyphenol content and DPPH radical scavenging activity were increased by fermentation and, especially, cordycepin content increased by 24%, which implies the enhanced functional property of the fermentation product.