In the course of our screening program for new antibiotics with spheroplast formation, nitracidomycins A (la) and B (lb) were obtained from the culture filtrate of a streptomycete. They were characterized and shown to have a nitronic acid and an 4-amino-3 hydroxy acid moiety in their structures; they both had moderate activities against Gram-positive bacteria and some species of Gram-negative bacteria, such as Bacteroides fragilis. In this report, the production, isolation, physicochemical properties, structures and biological properties of la and 1b are reported.