A novel antifungal antibiotic, YM-193221, was found in the culture broth of a fungus, Pseudallescheria ellipsoidea. The structure of the antibiotic was determined through several spectroscopic experiments as 2-dimethylamino-1-(4-hydroxyphenyl)-8,10-dimethyl-6-dodecene-3-one. YM-193221 exhibited potent antifungal activity against Candida albicans and also inhibited mannan synthesis in the yeast cell wall.