Abstract: Objective To analyse the causes related to sputum positive conversion in patients pulmonary tuberculosis during regular treatment.  Methods The data of sputum positive conversion in 53 patients with pulmonary tuberculosis during regular treatment was analyzed retrospectively.  Results Of 53 patients, 18 patients had sputum positive conversion. 8（44.4%） cases became sputum positive at the second month, which included 3（16.7%） cases with primary drug resistance.2 （11.1%）cases and 8 （44.4%）cases had sputum positive conversion at the third month and the fifth month respectively. In addition, there were 35 cases with smear and culture positive before treatment among 53 cases. 13 （37.1%）cases had sputum positive conversion in the third month,12 （34.3%） cases in the fifth month, and 8 （22.9%）cases, which 3 （7.7%）cases were progressive and 1 case with drug resistant was given high dose hormone due to immulogocial disease, were in the sixth month. There were another 2（5.7%） cases sputum positive conversion at the eighth month. The major factors which affect sputum positive conversion in patients with endobronchial tuberculosis, drug resistance, diabetes mellitus and retreatment.  Conclusion s It should be emphasized on monitoring sputum bacteria and finding cases with sputum positive conversion timely durmg the chemotherapy of tuberculosis.

Key words: tuberculosis pulmonary/therapy, sputum/mierobiolgy, treatment outcome