A new antibiotic, cispentacin, was isolated from the culture broth of a Bacillus cereus strain, L450-B2. The antibiotic is water-soluble and amphoteric; its structure was determined by spectroscopic analysis and chemical synthesis to be (1R,2S)-2-aminocyclopentane-1-carboxylic acid. Cispentacin demonstrated only weak in vitro activity against certain fungi but strong protection of mice from lethal infection of Candida albicans A9540.