The metabolic syndrome (MS) is a cluster of risk factors for cardiovascular disease related to insulin resistance. Recently, serum gamma glutamyltransferase (GGT) has been proposed as a marker of oxidative stress and is associated with a marked increase in the risk of cardiovascular disease. So, we investigated the association between serum GGT and components of the metabolic syndrome in the Korean adults. A total 3246 adults (aged 20-70 years, 1622 men and 1624 women) who visited Center for Health Promotion in Pusan National University Hospital for a medical checkup were included. We measured serum GGT and lipid profiles, fasting glucose, fasting insulin and blood pressure. As the quartile of serum GGT increased, the number of components of MS and prevalence of MS were increased. Serum GGT was also increased according as the number of components of MS was increased. A significant correlation (r=0.200, p<0.001 in men and r=0.133, p<0.001 in women) was noted between the numbers of the components of the MS and serum GGT. In addition, serum GGT was correlated significantly (r=0.266, p<0.001 in men and r=0.264, p<0.001 in women) with homeostasis model assessment of insulin resistance (HOMA-IR). In linear regression model, serum GGT was mainly influenced by the concentration of triglycerides and fasting glucose. In conclusion, serum GGT is closely related with insulin resistance and the increased number of components of MS. Among components of MS, serum GGT may be more associated with dyslipidemia and abnormal glucose tolerance, suggesting that serum GGT has more relationship with hepatic insulin resistance regardless of non-alcoholic fatty liver disease.