The local treatment of atrophic rhinitis with estrogen first has been described by Mortimer, Wright, Collip in 1937. Soskin and Bernheimer have pointed out the good results reported with the use of atrophic rhinitis were due to the secondary hyperemia associated with direct nasal application of estrogens. The authors performed an experimental study with the repeated instillation of nasal drop into the nasal cavity of rabbits during a period 1 month to 3 months, and effect of estrogen nasal drop on mucosal changes were correlated with histopathologic findings. The following results were obtained. 1) A histopathologic alteration of anterior part of respiratory mucosa in rabbit was more apparent than posterior part. The principal histopathologic changes were noticed superficially. 2) Major histopathologic changes encountered in the respiratory mucosa included ciliated epithelial hyperplasia, squamous metaplasia, goblet cell hyperplasia, basal cuboidal cell proliferation, serous gland ectasia, marked edema & congestion, and increased infiltration of inflammatory cells. Above mentioned findings revealed a tendency to be increased relating to the experimental period. 3) The lymphocyte and plasma cell was diffusely infiltrated under the mild degree. Irreversible and permanent changes were not recognized during a period of experimental months.