Metabolic syndrome (MetS) is a cluster of cardiovascular risk factors, usually with a common pathophysiological origin in insulin resistance and abdominal obesity. Considering the reported effects of ellagic acid (EA) on insulin resistance and abdominal obesity, the aim of this study was to evaluate the effect of EA on the components of MetS, insulin sensitivity and insulin secretion by conducting a randomized, double-blind, placebo-controlled, clinical trial with 32 volunteers diagnosed with MetS. Sixteen patients were randomly allocated, received 500 mg of EA orally twice a day for 12 weeks, and the other 16 received a placebo. Clinical and laboratory determinations were obtained at baseline and at the end of the study. After EA administration, patients reduced their waist circumference (females: 102.2 ± 4.2 to 99.5 ± 3.2 cm (p < 0.05); males: 99.8 ± 6.7 to 96.0 ± 4.7 cm (p < 0.01)), systolic blood pressure (118.1 ± 10.1 to 113.7 ± 7.8 mmHg (p < 0.01)), diastolic blood pressure (118.1 ± 10.1 to 113.7 ± 7.8 mmHg (p < 0.01)), triglycerides (2.8 ± 1.1 to 2.1 ± 0.7 mmol/L (p < 0.01)), fasting plasma glucose (6.5 ± 0.5 to 5.7 ± 0.6 mmol/L (p < 0.01)), fasting plasma insulin (p < 0.01), and insulin secretion (p < 0.05), with an increase of insulin sensitivity (p < 0.01). In male patients, high-density lipoprotein cholesterol increased (p < 0.05). In conclusion, EA improved the components of MetS, reduced hyperinsulinemia, and improved insulin sensitivity.