A new antifungal diketopiperazine named haematocin was isolated from the culture broth of Nectria haematococca Berk. et Br. (880701a-1) causing blight disease on ornamental plants, Phalaenopsis spp. and Doritanopsis spp. Its structure was established by spectroscopic methods. Haematocin inhibited the germ-tube elongation and spore-germination of Pyricularia oryzae at the ED50 values of 30 microg/ml and 160 microg/ml, respectively.