Objective To study serum IL-22 levels in patients with pulmonary tuberculosis and diabetes mellitus (PPTDM) and to analysis their clinical significance.Methods ELISA was used to detect serum IL-22 levels in 30 cases PPTDM pa-tients,30 cases pulmonary tuberculosis (PTB)patients,30 cases diabetes mellitus (DM)patients and 30 cases healthy vol-unteers (HV).Results Serum IL-22 levels of PPTDM patients (54.4±4.81 pg/ml)were significantly lower than those in diabetes mellitus (DM)patients (72.36±5.12 pg/ml)and healthy volunteers (HV)(68.32±3.08 pg/ml)(t=2.557,P =0.013;t=2.437,P =0.018),respectively.There was no significantly different of serum IL-22 levels between PPTDM and PTB patients (t=1.190,P =0.239).Serum IL-22 levels of diabetes mellitus coincident with pulmonary tuberculosis (DM-PTB)patients (64.62±8.59 pg/ml)were significantly higher than those in pulmonary tuberculosis coincident with diabetes mellitus (PTB-DM)patients (44.21±2.68 pg/ml)(t=2.267,P =0.031).Conclusion IL-22 may play an important role in PPTDM development.