This study investigated the effect of exercise training on insulin resistance and serum and adipose TNF-a in high-fat diet-induced insulin-resistant rats. Thirty male Wistar rats were randomly divided into two groups: normal control group (NC; n=8) that accepted normal chow and high-fat diet group (HF; n=22) that fed on high-fat diet to induce insulin resistance model. The HF group was randomly assigned to two subgroups after 18 weeks: sedentary group (SE; n=10) and exercise training group (ET; n=12) that performed swimming exercise training for 6 weeks, while both groups continued high-fat diet. Changes of body weight, lipid profile, and fasting plasma glucose and insulin were measured. The insulin sensitivity index (ISI) was calculated. Serum concentration of TNF-α was detected by ELISA. The expression of TNF-α mRNA and protein in adipose tissue was examined by using real-time fluorescence quantitative polymerase chain reaction (PCR) and Westem blot, respectively. After 18 weeks, compared with the NC group, body weight, blood lipid, glucose, and insulin in the HF group were significantly elevated, while the ISI decreased obviously, which suggested that insulin resistance appeared in the HF group. After exercise training for 6 weeks, compared with the SE group, both ISI and serum TNF-α concentration in the ET group were decreased significantly; however, the expression levels of TNF-α mRNA and protein in adipose tissue increased by 27.5% and 20.5%, respectively. In conclusion, exercise training ameliorates insulin resis-tance. The reduction of the level of serum TNF-α and the increased expression of TNF-α in adipose tissue by exercise training may be involved in this mechanism.