Background: functional endoscopic sinus surgery, (FESS), is a minimally invasive surgical procedure that opens up the paranasal sinus ostia with an endoscope. Endoscopic sinus surgery is seen as the standard treatment in chronic rhinosinusitis and Sinonasal polyposis. Objective: it was to assess the efficacy of intra and postoperative topical application of Mitomycin C after endoscopic sinus surgery in reducing adhesions and scar formation and improving outcome of FESS. Patients and Methods: this study included 60 cases (24 female (40%) and 36 male (60%) ranging in age from 18 to 50 years) with mean 34 bilateral chronic rhinosinusitis with or without sinonasal polyposis undergoing functional endoscopic sinus surgery. Every patient in this study had been submitted for full history taking, general examination, full ENT examination routine preoperative laboratory investigations and computerized tomography study on the nose and paranasal sinuses. Functional endoscopic sinus surgery had been done for all patients. Results: In our study, bilateral nasal obstruction was presented in 46 patients (76.6%), anterior nasal discharge was presented in 22 patients (36.6%), posterior nasal discharge was presented in 18 patients (30%), headache was presented in 40 patients (66.6%) and facial pain was presented in 12 patients (20%). Endoscopic assessment of the patients 2 months after F.E.S.S revealed that the adhesions presented in 32 sides (26.7%) mainly occurred on the control side 25 (41.7%) while the Mitomycin C side showed minimal adhesions 7 (11.7%) with significant P value (0.04). Conclusion: Topical application of MMC at end of FESS has beneficial role in prevention of adhesion formation and synechiae without any side effects/complications.