AbstractBackground:  Type IV collagen, a heterotrimeric molecule that exists in six genetically distinct forms, α1(IV)–α6(IV) is a major structural component of basement membrane (BM) and acts as a scaffold for other BM constituents.Methods:  Indirect immunofluorescence using α chain‐specific monoclonal antibodies was employed to clarify basement membrane (BM) collagen IV distribution in two ameloblastoma, and for comparison, on oral mucosa and tooth germ.Results:  Ameloblastoma BM expressed five of six genetically distinct forms of collagen IV: α1(IV), α2(IV), α5(IV) and α6(IV) chains occurred as intense linear stainings without disruption around neoplastic epithelium, and this expression pattern was fundamentally similar to oral mucosa BM; α4(IV) expression was rare and occurred around nests of primitive tumor cells or potentially invasive sites. The tooth germ demonstrated a stage‐ and position‐specific collagen IV distribution: the inner enamel epithelium BM expressed α1(IV), α2(IV), and α4(IV) except in the cuspal predentine region; and the outer enamel epithelium BM expressed α1(IV), α2(IV), α5(IV), and α6(IV) chains.Conclusions:  Results suggest that collagen IV α chain distribution in ameloblastoma BM plays an important role in tumor cytodifferentiation and progression.