Macrophages in the lungs are the most important cell type supporting replication of Mycobacterium tuberculosis in humans. The objective of this study was to investigate whether the effect of moxifloxacin against M. tuberculosis residing in macrophages could be improved by encapsulation of the drug in the biodegradable nanoparticles, which are known to accumulate in macrophages upon intravenous administration. To accomplish this, moxifloxacin was encapsulated in poly(butyl cyanoacrylate) (PBCA) nanoparticles. Encapsulated moxifloxacin accumulated in macrophages approximately three-fold times more efficiently than the free drug, and was detected in the cells for at least six times longer than free moxifloxacin at the same extracellular concentration. Inhibition of intracellular M. tuberculosis growth with encapsulated moxifloxacin was achieved at the concentration of 0.1microg/ml, whereas the same effect with free MX required a concentration of 1microg/ml. Nanoparticles observed within the macrophage cytoplasm were distributed throughout the cytoplasm, sometimes in the vicinity of intracellular bacteria.