AIM: To investigate the variation and distribution of abnormaly methylated p15 INK4B in myelodysplastic syndrome (MDS) and its subgroups. METHODS: The abnormal methylation of p15 INK4B in 32 cases with MDS was studied using methylation-specific PCR (MSP). RESULTS: The positive rate of abnormal methylation of p15 INK4B was about 50% in MDS. The ratios in subtypes were: 0% (0/6) in RA,20% (1/5) in RA-S,57.1% (4/7) in RAEB,74.1% (5/7) in CMML,85.7% (6/7) in RAEB-t, respectively.It was worth noticing that 4 cases represented abnormal methylation of p15INK4B during their transformation and progression into AML. CONCLUSION: The abnormal methylation in p15 INK4B might be one of the causes of MDS, which was related to pathologial process of MDS.Every subtype was not solitary classification completely. Abnormal methylation of p15 INK4B was apt to occur accompanying the progression and transformation of the subtypes.