Abstract: Objective: To explore the clinicopathological and immunohistoche mical features of primary anorectal malignant melanoma(AMM) as well as its diagnosis and prognosis.Methods: The clinical pathological characteristics of 9 cases of AMM were observed.All the cases were studied by immunohistochemical technique.Results: The clinical manifestations of the 9 cases of AMM were bloody stool,bloody purulent stool,and alteration of bowel habit and bowel trait.Polypoid type tumors were observed in 3 cases,protrude type with ulcer in 4 cases and ulcer type in 2 cases.The histopathological feature of primary melanoma was similar to that of the skin melanoma were classified into epithelioid cell type 5 cases,spindle cell type 1 case,small cell type 2 cases and hemangiopericytoma-like type 1 case.In the immunophenotype melanoma,positive fos-related antigen HMB45 was observed in 8 cases,positive S-100 in 9 cases,positive melanoma-A(MELAN-A) in 7 cases and positive vimentin in 8 cases.No significant difference in the clinicopathogical features and the expression of antigens were observed between the AMM and the skin melanoma.Conclusions: AMM is a rare and highly malignant tumor with poor prognosis and easily misdiagnosed.Detection of HMB45,S-100 and MELAN-A protein may be of help to the diagnosis and differential diagnosis of the tumor.