Abstract Background: The aim of this study was to evaluate the effect of berberine administration on metabolic syndrome, insulin sensitivity, and insulin secretion. Methods: A randomized, double-blind, placebo-controlled clinical trial was carried out in 24 patients with a diagnosis of metabolic syndrome. Glucose and insulin levels after a dextrose load were measured. Triglycerides and high-density lipoprotein cholesterol concentrations at baseline were also measured. Twelve patients received berberine hydrochloride (500 mg) three times daily before meals for 3 months. The remaining 12 patients received placebo. Area under the curve (AUC) of glucose and insulin, total insulin secretion, first-phase of insulin secretion, and insulin sensitivity were assessed. Results: After berberine administration, patients had a remission of 36% (P=0.037) in the presence of metabolic syndrome and a significant decrease in waist circumference in females (106±4 vs. 103±3 cm, P<0.05), systolic blood pressure (SBP) (123±7 vs. 115±9 mmHg, P<0.01), triglycerides (2.4±0.7 vs. 1.4±0.5 mmol/L, P<0.01), area under the curve (AUC) of glucose (1182.1±253.6 vs. 1069.5±172.4 mmol/l, P<0.05), AUC of insulin (92,056±72,148 vs. 67,407±46,441 pmol/L, P<0.01), and insulinogenic index (0.78±0.69 vs. 0.62±0.46, P<0.05), as well as an increase in the Matsuda index (2.1±1.0 vs. 3.1±1.6, P<0.01). Conclusions: Administration of berberine leads to remission of metabolic syndrome and decreases in waist circumference, SBP, triglycerides, and total insulin secretion, with an increase in insulin sensitivity.