Abstract Extractable glycolipids of mycobacteria, such as lipooligosaccharides (LOS), play key roles in responding to environmental stress and altering the host immune response. However, although the biosynthesis of LOS is likely controlled at multiple levels to ensure proper composition of the cell wall, the key regulators are currently unknown. Here, we studied B11, a conserved mycobacterial sRNA, and found that it post-transcriptionally regulates LOS synthesis in Mycobacteria marinum.