A new antibiotic, leucinostatin, was isolated from the culture filtrate of Penicillium lilacinum. The antibiotic was obtained in the form of white prisms, decomposing at 131-136°C, and showing optical rotation [α]22D+644° (c 0.5, methanol). The ultraviolet absorption spectrum showed only an inflection at 220 nm in methanol. The antibiotic gave a positive reaction to biuret and negative to ninhydrin. Upon hydrolysis, it gave a positive reaction to ninhydrin, yielded leucine predominantly, and the peptide nature of the antibiotic was assumed. Leucinostatin was found to be active against some gram-positive bacteria and a wide range of fungi. It was also cytotoxic to HeLa cell culture and showed some inhibitory effect on EHRLICH subcutaneous solid tumor. The LD50 by intraperitoneal injection in mice was calculated to be 1.6 mg/kg. The antibiotic manifested a significant hypotensive effect on rabbit blood pressure without affecting epinephrine and acetylcholine responses.