Histiocytic sarcoma(HS)is a rare malignant neoplasm that originates from a histiocytic hematopoietic lineage characterized by histiocytic differentiation and its corresponding immunophenotypic features.We herein reported a case of primary HS of the stomach which was confirmed through histopathologic examination and immunohistochemical staining.A 52-year-old woman presented with progressive difficulty in feeding and dull pain in the epigastric region.Gastroscopy,endo-scopic ultrasonography,double contrast examination, and computed tomography revealed a mass located on the posterior wall of fundus and lesser curvature of the stomach.Microscopically,the cytoplasm of the tumor cells was abundant and eosinophilic.Immunohisto-chemical staining revealed that the tumor cells were positive for CD45RO and CD68.It is difficult to differentiate HS of stomach from other gastric malignancies by radiological evaluation alone.However,HS may be considered when a protruding and ulcerated mass in stomach shows heterogeneous hypervascular features.To the best of our knowledge,this is the first report in English language literature that emphasizes the imaging findings of human gastric HS. Histiocytic sarcoma (HS) is a rare malignant neoplasm that originates from a histiocytic hematopoietic lineage characterized by histiocytic differentiation and its corresponding immunophenotypic features. We reported reported a case of primary HS of the stomach which was confirmed through histopathologic examination and immunohistochemical staining. A 52 -year-old woman presented with progressive difficulty in feeding and dull pain in the epigastric region. Gastroscopy, endo-scopic ultrasonography, double contrast examination, and computed tomography revealed a mass located on the posterior wall of fundus and lesser curvature of the stomach. Microscopically, the cytoplasm of the tumor cells was abundant and eosinophilic. Immunohisto-chemical staining revealed that the tumor cells were positive for CD45RO and CD68. It is difficult to differentiate HS of stomach from other gastric malignancies by radiological evaluation alone. be considered when a protruding and ulcerated mass in stomach shows heterogeneous hypervascular features.To the best of our knowledge, this is the first report in English language literature that emphasizes the imaging findings of human gastric HS.