OBJECTIVE: To evaluate the effect of Persian shallot extract on the serum markers and blood pressure of patients with metabolic syndrome (MetS). METHODS: Fifty patients with MetS diagnosis were randomly assigned to the intervention (Persian shallot extract) and the control (placebo) group. Both groups received treatment for three months. Before the study and at the end of the study, 5 mL peripheral blood was taken from each patient. The measured factors included total antioxidant capacity (TAC), superoxide dismutase enzyme (SOD), malondialdehyde, oxidized low-density lipoprotein (Ox-LDL), apolipoprotein H (Apo-H), fasting blood glucose (FBS), total cholesterol, triglycerides, high-density lipoprotein (HDL), LDL, and systolic and diastolic blood pressure. RESULTS: At baseline, the evaluated parameters were not significantly different between the intervention and control groups. At the end of the study, the mean serum levels of malondialdehyde and ox-LDL were significantly lower in the intervention group. The mean FBS, cholesterol, triglycerides, and LDL were significantly lower in the intervention group. The mean TAC and HDL were significantly higher in the intervention group ( CONCLUSION: Persian shallot extract has several beneficial effects in MetS patients, including optimizing oxidative balance, reducing blood pressure, fasting blood sugar, and blood lipid profile.