Objectives: evaluate of outcome of surgery using microdebrider compared to conventional endoscopic sinus surgical instruments in the management of sinonasal polyposis. Study Selection: This prospective randomized comparative study was conducted on 40 patients presented to ENT department at Al azhar university hospital-Assuit, diagnosed clinically and radiologically as bilateral sinonasal polyposis not responding to medical treatment. These patients were divided into two groups, 20 patients for each group. The first group Group A (microdebrider group) was operated using microdebrider and the second group Group B (standard Group) was operated using Messerklinger technique described by Stammberger using conventional instruments. Data Synthesis: Data were collected, coded, revised and entered to the Statistical Package for Social Science (IBM SPSS) version 20. Findings: There is a significant difference in intraoperative blood loss among both group. The intraoperative blood loss was significantly lower among patients who were operated with Microdebrider assisted FESS (Group A). The mean time of surgery in Group A was 120 minutes while the mean time of surgery in Group B was 173 minutes. Conclusion: The use of microdebrider in endoscopic sinus surgery for patients with sinonasal polyposis has the advantage of dry operative field with better visualization and shorter operative time when compared to endoscopic surgery with the conventional instruments.