To study the effects of sodium valproate (VPA) on human myelodysplastic syndrome cell line MUTZ-1. The cell proliferation was determined by MTT assay, apoptotic morphological features were observed by light microscopy and transmission electronmicroscopy, cell apoptosis and cell cycle shift were analyzed by flow cytometry (FCM). The results showed that VPA could inhibit the growth of MUTZ-1 cells in dose-and time-dependent manners. The typical apoptotic morphological features appeared in MUTZ-1 cells treated with 4 mmol/L VPA for 72 hours. Pyknosis of cells and nuclei, disintegration of nuclear chromatin and apoptotic body could be observed by light microscopy. Aggregation and margination of nuclear chromatin, concentration of plasm, increment of density and chromatin mass of irregular size could be observed by transmission electronmicroscope. The flow cytometric analysis indicated that the VPA could induce cell apoptosis, apoptosis rate increased in dose-dependent manner, ratio of cells at G(0)/G(1) phase increased and ratio of cells at S phase decreased in dose-dependent manner, the cells were arrested at G(0)/G(1) phase. It is concluded that the VPA can induce apotosis and inhibite proliferation of MUTZ-1 cells via arresting cells at G(0)/G(1) phase.