Functional Endoscopic Sinus Surgery (FESS) is a common day surgery technique for upper airway disorders. Hyaluronic acid (HA) is a fundamental component of the human connective tissue. HA may exert reparative, anti-inflammatory and immune-modulating activities. Recently, a new intranasal HA formulation has been proposed: a supramolecular system containing lysine hyaluronate, thymine and sodium chloride (T-LysYal®). This randomized study investigated whether intranasal T-LysYal® (RinoLysYal®, Farmigea, Italy) was able to reduce symptom severity, endoscopic features, and nasal cytology in 83 patients (49 males and 34 females mean age 45.4±6.2 years) treated with FESS. All patients were treated with isotonic saline solution for 4 weeks, and a sub-group (active group) was also treated with intranasal T-LysYal®. Patients were visited at baseline, after treatment, and after 4-week follow-up. Intranasal T-LysYal® treatment significantly reduced the quote of patients with symptoms, endoscopic features, and inflammatory cells in comparison to isotonic solution. In conclusion, the present study demonstrates that intranasal T-LysYal® is able to significantly improve patients after FESS and its effect is long lasting.