To investigate the anti-proliferative effects of an aqueous extract of Cordyceps militaris (AECM) on the growth of human lung carcinoma cell line A549, we performed various biochemical experiments such as the effects of AECM on the cell proliferation and viability, the morphological changes, the effects on expression of apoptosis and cell growth-regulatory gene products. Results obtained are as follow; AECM treatment declined the cell viability and proliferation of A549 cells in a concentration-dependent manner. The anti-proliferative effect by AECM treatment in A549 cells was associated with morphological changes such as membrane shrinking and cell rounding up. Taken together, these findings suggest that AECM-induced inhibition of human lung cancer cell proliferation is associated with the induction of apoptotic cell death via regulation of several major growth regulatory gene products, and C. militaris may have therapeutic potential in human lung cancer.