Obesity is associated with numerous immunological disorders. The present study investigated the proportion and phenotype of myeloid‑derived suppressor cells (MDSCs) in the plasma of obese subjects and the association of these cells with the level of liver enzymes. Certain features of the immune response in obese subjects were examined by analyzing the expression of T cell receptor‑ζ (TCRζ) molecules on the surface of T cells. The expression and secretion of S100A9, a possible marker for MDSCs, were detected in the peripheral blood of obese subjects and compared with levels in lean controls. Results showed that the percentage of monocytic MDSCs, with the phenotype CD33+CD11b+CD14+HLADRlow/‑, was significantly increased in obese subjects compared with lean controls. The circulating level of monocytic MDSCs was positively correlated with the levels of liver enzymes in serum. The expression of the TCRζ molecule in the resting T cells was significantly lower in obese individuals than that of lean controls. The expression of S100A9 was detected in the majority of monocytes in peripheral blood mononulear cells, but no difference was identified in the frequency of CD14+S100A9+ cells between the obese and lean groups. However, the plasma level of S100A8/9 was significantly increased in obese compared with lean subjects. These observations suggested that the increased frequency of CD33+CD11b+CD14+HLADRlow/‑ cells may be responsible for the impaired T‑cell function and liver injury observed in obesity.