ABSTRACT. This study aimed to examine olfactory mucosal changes in a rat model of acute rhinosinusitis and to determine how acute rhinosinusitis induces dysosmia. Total 100 rats were divided into the experimental (N = 80) and control (N = 20) groups. An acute rhinosinusitis model was established in the experimental rats. From the experimental group, 20 rats each were sacrificed at 1, 2, 3, or 4 weeks. The control group was sacrificed at 1 week without inoculation. Olfaction was tested by the buried food pellet test before killing the rats, and the duration until the pellet was recorded and analyzed by a statistical software program. Mature olfactory receptor neurons (ORNs) and olfactory ensheathing cells (OECs) were examined. The durations spent by the experimental group in the BFPT were 402.9 ± 9.3, 453.7 ± 7.3, 351.9 ± 8.9, and 278.7 ± 8.1 s at 1, 2, 3, and 4 weeks, respectively. These durations were greater than that of the control group (178.3 ± 6.6 s), and the difference was statistically significant (P < 0.01). A reduction in ORNs and thinning of the epithelium were detected in the experimental group, most notably in the 2nd week and less in the fourth week. OECs were reduced in the 1st week, increased in the 2nd week, and almost completely recovered in the fourth week. In addition, some growing OECs were detected in the experimental group. Acute rhinosinusitis decreased both the mature ORNs and OECs, but OECs increased faster than the ORNs.