Cordyformamide (4), the plausible biogenetic precursor of xanthocillin Y2, was isolated from a culture broth of the insect pathogenic fungus Cordyceps brunnearubra BCC 1395. Cordyformamide was found to exhibit activity against the malarial parasite Plasmodium falciparum K1 with an IC50 value of 18 microM, whereas it showed weak or no cytotoxicity.