The structures of epoxyquinomicins A (1), B (2), C (3) and D (4) were determined by spectroscopic studies. Compound 1 was determined to be (5R,6S)-2-(3-chloro-2-hydroxybenzoylamino)-5-hydroxymethyl-5,6-epo xy- 2-cyclohexene-1,4-dione. Compound 2 was revealed to be the dechlorinated derivative of 1. Compounds 3 and 4 were determined to be the reduced derivative of 2 and 1, respectively.