Objective:To investigate the expression of DNA methylation transferase 1 (DNMT1) and histone deacetylase 1 (HDAC1) proteins in intraductal papillary mucinous neoplasms (IMPNs) and its possible clinical significance.Methods:The presence of DNMT1 and HDAC1 proteins in the 48 IPMNs and 54 pancreatic ductal adenocarcinomas (PDACs) were examined using SP immunohistochemical method and were statistically analyzed.Results:The expression levels of both DNMT1 and HDAC1 increased in a malignancy-dependent manner:normal pancreatic ductal →IPMA,IPMB → IPMC → PDAC.And both of them were positive in IPMNs of different subtypes.Conclusion:Higher expression of DNMT1 and HDAC1 is an early event of pancreatic malignancy.Expression of them can reflect the malignancy transformation of IPMNs,but can not be used for histological typing of IPMNs.