Background: The SCR is an operational indicator for the DOTS strategy of Revised National Tuberculosis Control Programme (RNTCP) in india. The present study was undertaken to determine the relationship between sputum smear grading and smear conversion rate among the category I smear positive pulmonary tuberculosis patients undergoing DOTS. Methods: A prospective cohort study was carried out among category I pulmonary smear positive patients registered at the DOTS centres of District TB centre Karuvelipady, Government hospital Ernakulam ,Government hospital Paravur. The patients with pre-treatment sputum grading 3+ were placed in High positive cohort (HP cohort) and those with pre-treatment sputum grading as 2+,1+ and scanty were placed in Low positive cohort (LP cohort) were followed periodically at two months (end of Intensive phase ),at three months (after one month extension of Intensive phase),at two months of Continuation Phase and then at the end of the treatment to record the sputum AFB result and treatment outcome as per the RNTCP guidelines. Accordingly, a total of 397 category I patients with 213 in HP cohort and 184 LP cohort were enrolled in the study during November 2016 to January 2017. Data were analyzed using Medcalc Online calculator. Results: After two months (end of the intensive phase), SCR was 53.52% (114 of 213) among the High Positive and 69.56% (128 of 184) in the Low Positive cohort (p-0.001).After three months (one month’s extension of intensive phase),cumulative SCR was 74.17% (158 of 213) in the High positive and 84.25% (155 of 184) in the Low Positive cohort(p-0.01).Cure rate was 68.07% (145 of 213) in the High Positive and 77.71% (143 of 184) in the Low Positive cohort. Default rate was 23% (49 of 213) in the High Positive and 12.5% (23 of 184) in the Low Positive cohort. Failure rate was 3.28% (7 of 213) in the High positive and 4.89% in the Low positive Cohort (9 of 184).Twelve patients (5.63%) died in HP Cohort, nine patients in LP Cohort (p-0.23). Treatment outcome was further compared among the patients according to their sputum status achieved at two and three months of the treatment after ignoring their initial sputum status. The cure rates for the patients who converted at two months was 92.56% (224 of 242) and for those who did not convert at two months, was 55.65% (64 of 115) (p- 0.00001). Similarly, the cure rate for the patients who converted at three months was 78.04% (64 of 82) and for those who did not convert at three months was 0% (74) (p-0.00).