To examine the effect of xylitol nasal irrigation in a large sample size of patients who had undergone nasal surgery. Double-blinded randomized controlled crossover study. Tertiary referral center. The study included 100 patients with sinonasal disease who underwent endoscopic sinus surgery (ESS), septoplasty, or both concurrently. To identify patients with allergic sensitization, serum-specific immunoglobulin E levels were measured. Nasal symptoms were evaluated with the NOSE (Nasal Obstruction Symptoms Evaluation) and SNOT-20 (Sino-Nasal Outcome Test-20) and via visual analog scale (VAS) scores. In the ESS group (n = 34), the general nasal symptom score evaluated by the SNOT-20 showed significantly greater improvement in the xylitol group versus the saline group ( P = .022). VAS symptom scores for sneezing ( P = .003), headache ( P = .02), and facial pain ( P = .037) were also more improved in the xylitol group. In the septoplasty group (n = 39), the VAS score for nasal stuffiness showed a significantly greater improvement in the xylitol group when compared with the saline irrigation group ( P = .001). Among the patients with allergic sensitization (n = 31), rhinorrhea symptoms improved significantly more in the xylitol group than in the saline group ( P = .024). The preference survey showed that more than half of the patients in each surgical group preferred xylitol irrigation. We found that xylitol nasal irrigation was useful in postoperative ESS and septoplasty care. For patients with allergic sensitization, rhinorrhea showed greater improvement in the xylitol group than in the saline group.