Objective To detect the serum levels of retinol binding protein 4 (RBP4), adiponectin and tumor necrosis factor-alpha (TNF-α) in the patients with obesity and type 2 diabetes mellitus (T2DM), and to explore their correlations. Methods A total of 135 Chinese individuals living in Shanghai area were divided into the subjects with normal glucose regulation and normal body mass (NBM-NGR), overweight or obese subjects with normal glucose regulation (OW/OB-NGR), T2DM with normal body mass (NBM-T2DM) and T2DM with overweight or obesity (OW/OB-T2DM). The body fat, biochemical indices and the serum levels of RBP4, adiponectin and TNF-α were determined. Results Serum RBP4 levels were significantly higher in the subjects with T2DM and OW/OB-NGR than in those with NBM-NGR, and also in those with OW/OB-T2DM than in those with NBM-T2DM. Serum adiponectin levels were significantly lower in those with T2DM and OW/OB-NGR than in those of NBM-NGR. Serum TNF-α levels were significantly higher in those with T2DM than in those with NBM-NGR and OW/OB-NGR (P＜0.05 or 0.01). Spearman analysis indicated that RBP4 was negatively correlated to adiponectin but positively to TNF-α, and TNF-α had a negative correlation with adiponectin (P＜0.05 or 0.01). Multiple stepwise regression analysis showed that triglycerides (TG) and waist-hip ratio (WHR) were the independent risk factors for RBP4. TG, sex, hemoglobin A1c (HbA1c) and high density lipid protein-cholesterol (HDL-C) were the independent risk factors for adiponectin. HbA1c was the independent risk factor for TNF-α. Conclusion RBP4 is closely associated with abdominal obesity, but has no correlation with blood glucose. Adiponectin and TNF-α are mainly related to glucose metabolism. RBP4 is related with adiponectin and TNF-α.