Pepstatin A[1,2), an aspartyl protease inhibitor, is a potent new type of antifungal antibiotic[3). However, it is not clinically used because it is metabolized in the liver and rapidly cleared from the blood[4). As a result of our screening program for the search of Candida albicans aspartyl protease inhibitors, we reported on the new inhibitors, YF-0200R-A and B in a preceding paper[5). Subsequently we have isolated a new highly potent inhibitor, YF-044P-D (Fig. 1) which is produced by Streptomyces sp. YF-044P together with ahpatinin E, F and G[6). In this paper, we describe the fermentation conditions for YF-044P-D production,isolation procedure, physico-chemical properties, structural elucidation and biological activity of YF-044P-D.