Background: Malnutrition and tuberculosis are both problems of considerable magnitude in most of the underdeveloped regions of the world. Magnesium ion concentration of blood is inversely proportional to the type and extent of the disease which could possibly be due to chronic malnutrition and the amount and destruction of lung tissue in cases of pulmonary tuberculosis. This study is to see the effect of mycobacterium tuberculosis infection and antituberculosis treatment on serum magnesium level. Material & Methods: A hospital based longitudinal case control study done on all outdoor and indoor diagnosed patients of Pulmonary Tuberculosis (PTB), Multidrug-resistant Pulmonary Tuberculosis (MDRPTB) and healthy controls in IRD, Jaipur. 56 diagnosed cases of pulmonary tuberculosis before starting treatment (group PTB at initial) were followed after 2 months of treatment (group PTB at the end of intensive phage). 56 diagnosed case of multi drug resistant pulmonary tuberculosis (group MDRPTB). 56 age and sex matched healthy controls were taken and every candidate was examined for serum magnesium. Results: Our study showed that the maximum numbers of patients (54.76%) were in the age group of 31-50 years, male preponderance (57.14%). It was observed that Mg++ levels were signicantly decreases in PTB and MDRPTB cases as compared to control group. The Mg++ levels were also found to be signicantly lower in MDRPTB patients as compared to PTB patients (p=0.0047*). The mean value of serum magnesium level was signicantly lower in malnourished patients (1.575±0.012 mg/dl) compare to normal BMI patients (1.585±0.011 mg/dl), (p-value<0.001*) and was statistically signicant at initial in PTB group. The comparison of type of lesion & severity of disease with serum magnesium level was statistically signicant at initial and at the end of intensive phase in PTB group. Conclusion: We concluded that decreased serum magnesium is a constant nding during pulmonary tuberculosis. In order to better understand the role of magnesium in pulmonary tuberculosis further clinical studies are required. Randomized controlled trials are warranted to generate higher levels of evidences to support our ndings.