Cordyceps militaris has been known to produce an anticancer agent, cordycepin. Investigation on optimum culture condition for C. militaris had been performed. In the research program for discovering a novel function in the culture of C. militaris, the culture media was applied to a proliferation assays using various cell lines. The media showed significant anti-proliferative activities against al cell lines, especially to human leukemia cell line HL-60. The activity-guided purification of active ingredient was performed to obtain uracil. To the best of our knowledge, uracil has not been reported to possess anti-proliferative activity. However, the uracil obtained from the culture media was subjected to ICP-MS analysis to reveal that sodium, potassium and magnesium were found to co-exist with uracil, which might show anti-proliferative activity. Further study on the mechanism of the expression of the activity is now underway.