Background and Objectives：Mastoid obliteration surgery is a useful technique for otitis media either with or without cholesteatoma. Obliterating materials have to satisfy low antigenecity, less inflammation, little tissue resorption, high regeneration power and good integration into the host tissue. The aim of our study is to evaluate histopathological changes and effectiveness resulting from the different obliterating materials in the temporal dorsal bullae in rats. Materials and Method：We divided the rats into two groups. Group A was untreated, but group B underwent removal of mastoid mucosa with 2% trichloroacetic acid(TCA). Both groups had mastoid obliteration by the implantation of hydroxyapatite cement (Mimix®) and demineralized bone matrix (Regenafil®). Twelve weeks after the implantation, a histological study was performed to evaluate remaining implanted material, new bone formation and the formation of cysts within the bullae. Results：There was no or minimal inflammation or foreign body reactions in the mastoid obliteration groups with Mimix® and Regenafil®. In the obliterated group that was not treated with 2% TCA, the remaining implanted material with Mimix® group was more than in the Regenafil® group (p