Nourseothricin is a broad-spectrum antibiotic derived from Streptomyces noursei. In addition to being effective on prokaryotic cells of gram-positive and gram-negative bacteria, various fungi including Candida albicans, and certain DNA and RNA viruses, it is also effective on eukaryotic cells of higher eukaryotes. It has been used as a selection agent for cells containing the gene conferring resistance to it.

Although nourseothricin sulfate is a streptothricin antibiotic, it functions via a mechanism similar to that of the aminoglycoside antibiotics. It induces miscoding of mRNA and leads to inhibition of protein synthesis.