Abstract: Objective To investigate the correlation of serum exosomal microRNA (exomiR)-27a with drug resistance and adverse outcomes in pulmonary tuberculosis (PTB), to provide new evidence for the development of anti-tuberculosis treatment. Methods From May 2018 to June 2020, 326 patients with PTB in the Eighth Affiliated Hospital of Xinjiang Medical University were selected and divided into 228 patients with active TB (active group) and 98 patients with latent TB infection (latent group), and 100 healthy subjects were included as controls. The serum exosomes of all subjects were extracted and identified by transmission electron microscopy, nanoparticle particle size analyzer and flow cytometry. The expression level of serum exomiR-27a was detected by real-time quantitative PCR. The diagnostic value of serum exomiR-27a in PTB was analyzed by receiver operating characteristic (ROC) curve. Drug resistance in patients with active PTB was recorded after standard treatment. The effect of serum exomiR-27a on the incidence of adverse outcomes was analyzed. Results The characterization of serum exosomes confirmed that exosomes were successfully isolated from serum. Compared with the control group 0.92(0.63, 1.17), the expression of serum exomiR-27a was up-regulated in the active group 1.55(1.18, 2.09) and the latent group 1.27 (0.96, 1.65), and the expression of exomiR-27a in the active group was higher than that in the latent group (P<0.05). PTB patients with high serum exomiR-27a expression (≥1.50) had poorer chest radiography and a higher proportion of chronic hepatitis comorbidities (P<0.05). ROC curve analysis showed that the area under the curve (AUC) of serum exomiR-27a distinguishing control and active group was 0.838 (95%CI: 0.795-0.880) and the AUC of serum exomiR-27a distinguishing normal and latent group was 0.766 (95%CI: 0.701-0.830). Patients in the active group received standard antituberculosis therapy (≥6 months). The expression level of serum exomiR-27a in drug-resistant patients was higher than that in sensitive patients (P<0.001), and the expression level of serum exomiR-27a in multi-drug resistant tuberculosis patients was higher than that in single-drug resistant tuberculosis patients (P<0.001). Logistic regression analysis showed that elevated serum exomiR-27a was an independent predictor of PTB resistance (P<0.001). High expression of serum exomiR-27a indicated a higher incidence of adverse outcomes (log rank=15.725, P<0.001). Conclusions High expression of serum exomiR-27a is helpful in the diagnosis and prediction of adverse outcomes of PTB.