Abstract: Objective To investigate the methylation of Id4 gene promoter in patients with chronic leukemia. Methods MS-PCR was used to detect the methylation of Id4 gene in 9 chronic lymphocyte leukemia （CLL） patients and in 12 out of 18 chronic myelocytic leukemia （CML） patients, respectively. Id4 methylation was detected in bone marrow samples from health donors as normal controls. Results Methylation of Id4 gene was not observed in bone marrow samples from the healthy individuals, but observed in bone marrow samples from the 9 chronic leukemia patients. Conclusion Id4 methylation occurs at different extents in patients with CLL and CML. However, the ratio of Id4 methylation is different in patients with CLL and CML.