With he aim of abserving the ultrastructural changes in the nasal mucosa of guinea pigs with experimentally induced nasal allergy, the present study was made. We used 6 guinea pigs as allergy group, which were sensitized with ovalbumin. Another 6 guinea pigs were used as control group. Every guinea pig in allergy group had the titer of the specific IgE not less than 1 : 8, confirmed by passive cutaneous anaphylaxis reaction. Nasal mucosa was obtained from both inferior turbinates and observed by scanning and transmission electron microscopy. The results were as follows ; 1) The squamous epithelium, th transitional epithelium, the partly ciliated pseudostratified epithelium, and the pseudostratified ciliated columnar epithelium were observed anteroposteriorly in the inferior turbinate mucosa of both groups by scanning electron microscopy. In allergy group, less dense and shorter cilia without directionality were noted. It was also found that the basal cells or basement membrane were exposed because intercellular space was widened and the epithelial cells were lost in allergy group. 2) Transmission electron microscopy revealed that most granules of the mast cells in both groups were filled with the amorphous flocculent materials but a few granules in allergy group had become obscure, which was suggestive of degranulation, and that the eosinophils were migrating from the lamina propria to the epithelium with widened intercelluar space in allergy group. In conclusion, it was suggested that the epithelial injury occurred in the nasal mucosa of guinea pigs with nasal allergy.