Herbicidins A and B, two new antibiotics with selective and contact herbicidal activity, were produced by a new species of Streptomyces designated as S. sagononensis. Among tested microorganisms, herbicidins indicated some activity against fungi in vitro and Xanthomonas oryzae in vivo. Their characteristic features were brought into relief by their selective and contact killing effect on many dicotyledonous plant as well as their inhibition of germination of the plant seeds, such as Chinese cabbage.