INTRODUCTION: BPH is non–malignant and chronic progressive disease of men associated with LUTS. Several Studies have been conducted in men presenting with LUTS with BPH which demonstrated that PDE–5 inhibitors are efficacious both alone and in combination with an α–blocker in treating LUTS (4,5). This study is done to compare efficacy of Tadalafil and Tamsulosin with regards to BPH in cross over design. METHODS: In this randomized controlled prospective study, Men of 45 years age or older with LUTS with IPSS> 8 were screened. A total of 100 patients were included in study and devided into 2 groups. Group 1 patients were given Tamsulosin hydrochloride 0.4mg once daily in evening for a period of 6 weeks. Group 2 patients were given Tidalafil 5mg for a period of 6 weeks. Evaluation included clinical determination of IPPS, QOL, maximum flow rate, time to maximum flow, average flow rate, average flow time by uroflowmetry performed on uroflowmeter, postvoid residual urine volume and prostate size by USG at inclusion, 1 month and 3 month respectively. The findings in both groups were compared and statistically tabulated. RESULTS: 100 patients were screened and 40 patients were included in this study 20 patients were divided in 2 different groups. A total of 36 patients completed the study. Both drugs does not decrease prostate size however Tamsulosin improve post void residual while tadalafil did not. Both drugs do improve LUTS symptoms and uroflow parameters, but only tadalafil improve erectile dysfunction. CONCLUSION: The findings of the study showed if one drug do not show any clinical response to disease, it was changed to other drug, the patient responded to the PEDI ∝–blocker were not helped in relieving. Symptoms of LUTS and vice versa. Patient had significant response from Tadalafil in first groups for erectile days function. However, even Tamsulosin showed significant response in erectile dysfunction. There was significant improvement in IPSS voiding, when Tadalafil was crossed over to tamsulosin was changed over to tadalafil there was significant improvement in IIEF score