Rifampicin, also known as rifampin, is an ansamycin antibiotic used to treat several types of bacterial infections, including tuberculosis (TB), Mycobacterium avium complex, leprosy, and Legionnaires’ disease. It is almost always used together with other antibiotics with two notable exceptions: when given as a "preferred treatment that is strongly recommended" for latent TB infection; and when used as post-exposure prophylaxis to prevent Haemophilus influenzae type b and meningococcal disease in people who have been exposed to those bacteria. Before treating a person for a long period of time, measurements of liver enzymes and blood counts are recommended. Rifampicin may be given either by mouth or intravenously.

Common side effects include nausea, vomiting, diarrhea, and loss of appetite. It often turns urine, sweat, and tears a red or orange color. Liver problems or allergic reactions may occur. It is part of the recommended treatment of active tuberculosis during pregnancy, though its safety in pregnancy is not known. Rifampicin is of the rifamycin group of antibiotics. It works by decreasing the production of RNA by bacteria.

Rifampicin was discovered in 1965, marketed in Italy in 1968, and approved in the United States in 1971. It is on the World Health Organization's List of Essential Medicines. The World Health Organization classifies rifampicin as critically important for human medicine. It is available as a generic medication. Rifampicin is made by the soil bacterium Amycolatopsis rifamycinica.