Background: SMARCA4-deficient thoracic sarcoma is a recently proposed entity of soft tissue tumors associated with an extremely poor prognosis. Its cytologic features have not been well described in the literature yet. Case: A woman in her early 30s who presented with chest pain was found to have a tumor in the right chest wall. Cytologic smears revealed numerous atypical round-to-polygonal cells appearing singly or in loosely cohesive clusters. These cells had a well-defined cell border, scant-to-moderate cytoplasm, and enlarged vesicular nuclei with prominent nucleoli. In addition, some cells with eosinophilic globular intracytoplasmic inclusions and eccentrically located nuclei, consistent with rhabdoid cells, were observed. Immunocytochemically, the cells were at least focally positive for cytokeratin CAM5.2 and CD34 and showed a significantly reduced BRG1/SMARCA4 expression. The diagnosis was confirmed by histological, immunohistochemical, and genetic analysis of a metastatic lesion to the left axillary lymph node. Conclusion: Although the cytologic features of SMARCA4-deficient thoracic sarcoma are not fully unique, they are sufficiently characteristic to suspect this tumor in cases of supporting clinical and radiological features, which may promote additional immunological or molecular testing to establish a definitive diagnosis.