Background Hyponasality may be present in patients with chronic rhinosinusitis because of decreased resonance of nasal cavities. Nasalance is a parameter of nasality measured by a nasometer. This study investigated the influence of functional endoscopic sinus surgery (FESS) on nasalance and determined the correlation of the nasalance change with nasal volume change. Methods When patients with chronic rhinosinusitis underwent FESS, nasalance was measured by nasometry and nasal volume was measured by acoustic rhinometry before and at least 6 months after surgery. Results There were 81 eligible patients enrolled in the study. Nasalance scores and nasal volumes were significantly increased after FESS. The increased nasalance value was moderately correlated with the increased midnasal and postnasal volumes. The correlation between postoperative changes in nasalance scores and nasal volumes was more remarkable in patients without nasal polyps than in those with nasal polyps and it was also higher in patients with allergic rhinitis than in those without allergic rhinitis. Conclusion This study showed that the FESS effectively increased nasalance scores and nasal volumes in patients with chronic rhinosinusitis, but the increase in nasalance scores did not appear to be achieved largely through the increased nasal volumes.