Cordyceps militaris is used as medicinal mushroom with diverse activities, and contains cordycepin as a major bioactive constituent. The content of cordycepin is changed depending on the different sources of nutrition in the cultivation substrates. To investigate the optimal substrates for cultivation of fruiting body with high cordycepin content, thirty different species of grains were used to cultivate C. militaris. The stain Sejong043, which has been developed by C&G Agricultural Association Corporation, was used and the content of cordycepin was quantitated using HPLC analysis. Fruiting bodies of C. militaris were well induced in the grain mediums such as polished rice, glutinous rice, brown rice, barley, whole-wheat, oats, miliet, buckwheat, sorghum, sesame, perilla, and potatoes. The content of cordycepin was quite differential and was highest in the C. militaris grown on the brown lentil (3,406ppm) which followed by mung-beans (2,926ppm), cowpea (2,600ppm), brown-rice (2,537ppm) and horse-beans (2,536ppm). Conclusively, brown-rice was selected as an optimal substrate for both the growth of fruiting body and codycepin content of C. militaris.