Recently, it has become a struggle to treat tuberculosis with the current commercial antituberculosis drugs because of the increasing emergence of multidrug-resistant (MDR) tuberculosis and extensively drug-resistant (XDR) tuberculosis. We evaluated here the antimycobacterial activity of tamoxifen, known as a synthetic anti-estrogen, against eight drug-sensitive or resistant strains of Mycobacterium tuberculosis (TB), and the active intracellular killing of tamoxifen on TB in macrophages. The results showed that tamoxifen had antituberculosis activity against drug-sensitive strains (MIC, 3.125-6.25 μg/ml) as well as drug-resistant strains (MIC, 6.25 to 12.5 μg/ml). In addition, tamoxifen profoundly decreased the number of intracellular TB in macrophages in a dose-dependent manner.