In this work, ferrous sulfate was added into the C. militaris culture medium for stimulating cordycepin biosynthesis. The investigation on the gene expression of purine nucleotide pathway indicated that purA was highly up-regulated. This suggested that purA was a key gene in the cordycepin biosynthetic pathway. Although adenine or its derivatives could be converted to cordycepin in C. militaris In conclusion, ferrous sulfate was found as an efficient inducer for cordycepin biosynthesis