Objective: To compare the effectiveness of Tamsulosin in treatment of lower urinary tract symptoms (LUTS) in women. Design: Randomized double-blind placebo controlled trial Setting: Ramathibodi Hospital. Method: One hundred and fifty patients who were in eligible criteria at urological outpatient department were randomly allocated into 2 groups by block randomization. Group 1 received 0.2 mg of Tamsulosin and group 2 received placebo orally for 1 month in a double-blind fashion. Outcome variables included mean change of International prostate symptom score (IPSS), mean change of urinary flow rate and any adverse effect. Results: Mean change of IPSS (SD) were -5.2 (6.1) in Tamsulosin group and -2.8 (6.0) in placebo group. There was considered statistically significant. (exact p-value = 0.042) by Mann-Whitney U test. Mean change of urinary flow rate (SD) were 0.6 (2.6) ml/s in Tamsulosin group and -0.6 (2.5) ml/s in placebo group. There was considered statistically significant (exact p-value = 0.008). There were two patients in Tamsulosin group who had dizziness and asthenia. No any other adverse effect was detected. Conclusion: Tamsulosin was more efficacious than placebo in treatment of LUTS in women and should be used in selected female patients with LUTS.