Background: As men age, the prevalence of lower urinary tract symptoms (LUTS) linked with benign prostatic hyperplasia (BPH) rises. By the time they are 70 years old, almost 80% of men have been found to have BPH-related LUTS. LUTS, such as incomplete urination, frequency, urgency, nocturia, and reduced urine flow, appear in patients with BPH. Objective: We aimed to evaluate the efficacy and safety of single versus double dose of tamsulosin 0.4 mg for treatments of LUTS/BPH. Patients and methods: A double-blinded randomized controlled trial was conducted in the Outpatients Clinics for BPH-associated moderate and severe LUTS. Patients were randomized to receive single dose tamsulosin 0.4 mg capsule (1st group n = 33), and double dose tamsulosin 0.4 mg capsule (2nd group n= 32). The primary endpoints were the changes in International Prostate Symptom Score (IPSS), Uroflowmetry and PVR urine volume before starting the study, after one month and after 3 months of the treatment. Results: Total IPSS was more decreased (improved) in double dose tamsulosin 0.4 mg group than single dose tamsulosin 0.4 mg group, with P-value = 0.005 at one month follow up and 0.007 at three months follow up, which was statistically significant. However, dizziness was more frequent in double dose tamsulosin 0.4 mg group than in single dose tamsulosin 0.4 mg group (with P = 0.03 at one month follow up and P= 0.01 at three months follow up), which was statistically significant. Conclusion: Tamsulosin single and double doses had equal effects, safe, and well tolerated in the target BPH population. However, tamsulosin double doses was statistically superior to single dose in improving IPSS scoring. On the other hand, tamsulosin double doses had statistically significant adverse effect in the form of dizziness.