Nonalcoholic fatty liver disease (NAFLD) has been associated with metabolic disorders, including central obesity, dyslipidema, hypertension, and hyperglycemia. Metabolic syndrome, obesity, and insulin resistance are major risk factors in the pathogenesis of NAFLD. The aim of this study was to identify the relative contribution of the metabolic syndrome, obesity, and insulin resistance to alanine aminotransferase (ALT) activity in NAFLD. A total of 3091 subjects diagnosed with fatty liver by ultrasonography were enrolled. All components of metabolic syndrome criteria, anthropometric parameters, fasting insulin levels, high-sensitivity C-reactive protein (hs-CRP) as an inflammation marker, and ALT were measured in each subject. Homeostasis model assessment--insulin resistance (HOMA-IR) as a measure of insulin resistance and body mass index (BMI) as a measure of obesity were calculated. The prevalence of increased ALT levels (>40 IU/L) was 26.7%. Increased ALT activity was significantly associated with the following characteristics: male sex, young age, increased triglycerides, fasting glucose, fasting insulin, HOMA-IR, hs-CRP, waist circumference, BMI and diastolic blood pressure, and decreased high-density lipoprotein cholesterol (HDL-C). According to the increase in the number of metabolic syndrome components, BMI, HOMA-IR, and hs-CRP, the prevalence and odds ratio for having increased ALT activity were significantly increased. Central obesity, raised triglycerides, reduced HDL-C, and raised fasting glucose were strongly associated with increased ALT activity. In conclusion, a number of metabolic syndrome components, obesity, insulin resistance, and hs-CRP, are strong predictors of increased ALT activity in NAFLD. Central obesity, raised triglycerides, reduced HDL-C, and raised fasting glucose are metabolic syndrome components that contributed to increased ALT activity.