Objectives: In this study we aimed to investigate the prevalence of abnormal nasality in patients with unilateral rhinosinusitis and their nasality outcomes following functional endoscopic sinus surgery (FESS). Design, Setting, Participants: A total of 42 patients with unilateral chronic rhinosinusitis who underwent unilateral FESS between April 2016 and November 2017 were enrolled. The patients were divided into two groups, wide opening surgery and limited surgery, according to the severity of the disease. Questionnaires on sinonasal symptoms and nasality were recorded. Main outcome measures: The change in the nasalance score and symptoms were measured preoperatively, 6 months, and 12 months after the operation. Results: Among 42 patients, the subjective reports showed that one-third of unilateral chronic rhinosinusitis (CRS) patients had abnormal nasality preoperatively and significant improvement following FESS. The Lund-Mackay score was significantly negatively correlated with preoperative nasalance of [i] and positively correlated with change of nasalance of [i]. The increase in the value of [i] is statistically significant (p=0.01) following FESS. In the wide opening surgery group, the change in nasalance was significant, but not in the limited surgery group. Conclusion: Although only one side of the nasal airway was involved, one-third of the patients reported abnormal nasality. In patients with more disease severity who underwent wide opening surgery, the nasalance significantly increased 1 year after FESS. The increase in the nasalance score may represent a return to a normal status since the self-reported nasality assessment was significantly improved postoperatively.