Objective To investigate the efficacy of tamsulosin, a selective alpha-1 blocker, in lower urinary tract symptoms (LUTS) patients with metabolic syndrome (MS). Patients and Methods This prospective, multicenter clinical trial included men and women (20-75 years old) with LUTS, with or without MS. Patients were categorized as MS+ or MS-, respectively, and all of them were administered tamsulosin 0.2 mg per oral once daily for 24 weeks. Patients were assessed based on the International Prostate Symptom Score, King's Health Questionnaire (KHQ), Overactive Bladder Questionnaire, uroflowmetry with postvoid residuals, and MS factors (blood pressure, waist-to-hip ratio, and serum levels of fasting blood glucose, triglyceride, and high-density lipoprotein cholesterol) at baseline and at 4, 12, and 24 weeks of treatment. Results Ninety-two patients were enrolled in this study (53/92 were MS- [57.6%]; 39/92 were MS+ [42.4%]). After 24 weeks of tamsulosin treatment, fasting blood glucose (P =.02) and triglyceride (P <.001) levels of changes were significantly greater in the MS+ group than in the MS- group. Total International Prostate Symptom Score, total Overactive Bladder Questionnaire score, and the scores of each question on the KHQ showed significant improvement after treatment without intergroup differences. In KHQ, although improvements in emotional status, sleep quality, fatigue, and personal distress were greater in the MS+ group (P =.05), the difference between the groups did not reach statistical significance. Conclusion Tamsulosin was effective in both LUTS patients with and without MS. Furthermore, tamsulosin had beneficial effects on some of the factors associated with MS.