A 64-year-old man consulted for an abnormal shadow in November 2012. Chest computed tomography showed a thicking and small nodules of the left pleura and pleural effusion with mediastinal and supracravicular lymphnodes swelling. The cytological study of the pleural effusion showed individual atypical cells surrounded by many lymphocyte. The atypical cells are large, round or ovoid and had welldefined borders, abundant eosinophilic, glassy cytoplasm, and round or elliptic nuclei with clear eosinophilic nucleoli resembling decidua cells. According to immunohistochemistry study, cells were positive for calretinin, EMA, cytokeratinAE1/AE3, WT-1, D2-40 and negative for CEA, desmin, TTF-1, Ber-EP4, synaptophysin, S-100 compatible with deciduoid mesothelioma. The cytological features are important and useful for diagnosis of deciduoid mesothelioma.