Interleukin 38 (IL-38) is a new member of the IL-1 family, and it has anti-inflammatory activity. However, its role in type 2 diabetes mellitus (T2DM) has not been reported.The study included 40 T2DM patients and 42 healthy control subjects. The anthropometric and biochemical measurements were performed using an automatic biochemical analyser, high-performance liquid chromatography, and electrochemiluminescence immunoassay. Circulating IL-38 levels were determined by enzyme-linked immunosorbent assay.Serum IL-38 levels in T2DM patients were significantly lower than those in controls. Correlation analysis showed that serum IL-38 was negatively correlated with systolic blood pressure and interleukin 17 (IL-17).The results suggest that IL-38 may be a new biomarker of T2DM.