The objective of this study was to investigate the methylation status of zonula occluden protein-1 (ZO-1) gene in patients with myelodysplastic syndrome (MDS) and to identify its roles in pathogenesis, development and classification of MDS. 85 patients with MDS and 30 healthy individuals were tested by methylation specific polymerase chain reaction (MS-PCR). The results indicated that no ZO-1 promoter methylation could be detected in healthy controls. methylation of ZO-1 gene promoter of bone marrow was found in 56.5% (48/85) MDS patients. The difference between these two kinds of subjects was statistically significant (p<0.05). The methylation status of ZO-1 gene promoter region in the subtypes of MDS was as following: RA (18/37, 48.6%), RAS (4/6, 67%), RCMD (19/30, 63%), RAEB (7/12, 58%). Every subtype of MDS patients had statistical difference from healthy people (p<0.05), but between the subtypes of MDS there were no significant statistical differences in the methylation status of ZO-1 gene, while the level of ZO-1 promoter methylation in group of RA was lower than that in other groups. It is concluded that the ZO-1 promoter region in bone marrow of MDS patient shows a hypermethylation status, which is specific for MDS. MDS is a common hematologic malignancy with clonal proliferation, it is difficult to differentiate from many other hematologic malignancies in clinical diagnosis. However, the change of ZO-1 gene methylation status is closely related to pathogenesis of MDS, therefore the ZO-1 gene as valuable diagnostic marker has important clinical significance. The ZO-1 gene may be a potential gene related to hematologic malignancies.