Background: Tuberculosis is still a major health problem around the world. Malnutrition is frequently seen in TB patients. One of the important minerals being investigated in the malnutrition study is zinc. Deficiency of minerals in TB patients especially zinc has been reported in many cases. The aim of this study was to determine the effect of oral zinc supplements on the Sputum conversion of TB patients. Materials and Methods: This research was a randomized, double blind, placebo- control trial that was conducted in National Research Institute of Tuberculosis and Lung Disease (NRITLD). Patients with confirmed pulmonary tuberculosis having positive smears and cultures were divided by simple randomization into two groups i.e.: case and placebo groups. To the individuals of the case group, 0.5% zinc sulphate solution with a dose of 15mg/day was administered. Meanwhile in the placebo group, distilled water (as a placebo) with the same dose as zinc sulphate was given. Both groups received standard cat-Ι treatment. Patients from both groups underwent regular clinical investigation and smear test on days 0, 15, 30 and 60 and results were studied. Results: Out of 24 patients in the treatment group and 20 patients in placebo ,smears of 6 individuals (25 %) in case group and no individual in placebo group became negative at the end of fifteenth day (p <0.05). Smears of 17 (70.8 %) in intervention group and only 8 (40%) in placebo group became smear negative at the end of first month (p <0.05). At the end of second month, all patients in both groups became smear negative. Conclusion: According to the conclusions reached from this study, it seems that sputum conversion among the case group which used oral zinc sulphate supplement was much faster. (Tanaffos 2003; 2(7): 53-60)