Structures of novel anticoccidial antibiotics, cytosaminomycins A, B, C and D, were elucidated by NMR studies. Cytosaminomycins were shown to be nucleoside antibiotics related to oxyplicacetin. Their carboxylic acid moieties bonded to the cytosine residue were different from that of oxyplicacetin. The carboxylic acids contained in cytosaminomycins A, B, C and D were (E)-3-(methylthio)acrylic acid, 4-methylaminobenzoic acid, 3-methylcrotonic acid, and tiglic acid, respectively.