Objective: This study aimed to assess the role of local application of NAC post FESS in versus saline irrigation only. Patients and Methods: This study was a prospective, randomized controlled study that included 150 patients suffering from chronic allergic rhinosinusitis with nasal polyposis not responding to medical treatment. They underwent Functional Endoscopic Sinus Surgery, then they were enrolled in the study. They were divided into 2 groups, 75 patients per each group: The first group received N. acetylcysteine (NAC) nasal douches with saline irrigation for 3 weeks in the post-operative follow up period in contrast to the second group that received saline nasal irrigation only for a similar period. Results: After 6 weeks of follow up period the formation of nasal crusts, nasal adhesions and blood clots were observed in 5, 3 and 4 patients of the first group in contrast to 13, 10 and 12 patients from the second group consequently. Conclusion: Both NAC and saline irrigation promoted post-operative healing and prevented crusts formation, but combination between both of them resulting in better healing of nasal mucosa and prevented crusts formation and nasal adhesions.