Objective: To investigate the relation between eosinophilic materials and amyloid P (AP) component in adenomatoid odontogenic tumor (AOT). Methods: The expression of amyloid proteins and basement membrane proteins, including type Ⅳ collagen, laminin and heparin sulfate proteoglycan (HSPG), in AOT were analyzed by immunohistochemical method. Results:Most eosinophilic droplets among tumor cells and some epithelial cells showed positive stain for AP component.The immunoreactions of type Ⅳ collagen and laminin were only found in blood vessels of this tumor. The tumor cells and eosinophilic materials in duct-like structures were constantly unstained for both amyloid and basement membrane proteins. Present results suggest that the nature and composition of eosinophilic droplets may differ from the eosinophilic layer in ductlike structures. This study first demonstrated that the amyloid-like deposition in AOT is associated with AP component by immunohistochemical method. It supported that AP component may be epithelial origin since the AP immunolocalization was found in tumor cells.