This study aimed at evaluate Natural Killer (NK) cells in cases of pulmonary tuberculosis using flowcytometry. The present study comprised 50 subjects divided into two groups, the first group included 40 patients admitted at Chest Department - Kasr Al Anni hospital, Faculty of Medicine, Abbasia, and Giza chest hospitals, and those patients were subdivided according to response to antimycobacterium chemotherapy, into 4 (four) subgroups: Recently diagnosed (fresh), sputum convertor, sputum non convertor (after 8-10 weeks of treatment ), and relapsed (reactivation) subgroups.The second group included 10 normal persons as a control group. It was found that the percentage of CD56 (Natural Killer cells as a percentage of total lymphocytes) was significantly decreased in pulmonary tuberculosis .