<p>Olfactory dysfunction has been observed in asthma, but its underlying mechanisms are poorly understood. This prospective study assessed olfactory function using the YSK Olfactory Function Test in 30 patients with moderate to severe asthma, and compared clinical parameters according to changes in olfactory function over 6 months. Nine patients were classified into the olfactory-improvement group, 15 into the olfactory-stable group, and six into the olfactory-decline group. The change in blood eosinophil levels showed a progressive increase across the olfactory-improvement, olfactory-stable, and olfactory decline groups, while there were no significant differences in terms of the presence of upper airway diseases, use of intranasal steroids, asthma control status, and asthma treatment medications among the three groups. Eosinophilic inflammation in blood may be associated with olfactory function in asthma, and further study will be needed in the future.</p>