Metal-containing novel heterocyclic antibiotics, micacocidin A (1), B (2), and C (3) have been isolated from the culture filtrate of Pseudomonas sp. No. 57-250. The structure and absolute configuration of micacocidin A, an octahedral Zn²⁺ complex, was determined by X-ray crystallographic analysis. The structures of the two congeners, micacocidin B (Cu²⁺ complex) and C (Fe³⁺ complex), were investigated by one dimensional and two dimensional homonuclear and heteronuclear NMR spectroscopies and mass spectrometry. In the accompanied paper, the taxonomy, fermentation, isolation, physico-chemical properties, and biological activities of micacocidin A, B, and C were reported. Herein, we describe the structure determination of micacocidin A (1) and its two congeners (2 and 3), which are metal chelated antibiotics having specific and excellent activity against Mycoplasma species. Micacocidin A, B, and C were elucidated to be a zinc(II)-, copper(II)- and iron(III)-complexes with the same metal-free ligand, respectively. To the best our knowledge this is the first report of antimycoplasma agents having chelate structures from natural sources. They are different in both structure and activity from the known antibiotics and may be regarded as a novel class.