We report a case of peripheral primitive neuroectodermal tumor of the abdominal cavity in a 24-year old woman. Cytology of ascites consisted of numerous individualy scattered cells and a few small clusters. Tumor cells were small to medium size, with a high nuclear/cytoplasmic ratio. Their nucleoli were prominent. The histology of abdominal tumor in the abdominal cavity showed features similar to cytologic findings. An inmmunohistochemical study showed tumor cells were positive for MIC 2, vimentin, and cytokeratin. We showed the usefulness of immunohistochemistry in the cytology of this rare case.