This is a prospective (in which the patients are first identified and then followed forward as time passes), multi-center (study conducted at multiple sites), observational study (a scientific study to make a clear and easy understanding of the cause and effect relationship) to evaluate the effectiveness and safety information of a 5 day decitabine (Dacogen) regimen in patients with Myelodysplastic Syndrome. This study consist of 3 phases; pre-treatment phase, treatment phase and end of treatment (Day 28~61 after last administration of Dacogen). The patients will receive decitabine intravenous injection 20 mg/m2 one hour once daily for 5 consecutive days for every 4 weeks. Safety evaluations including adverse events and clinical laboratory tests and will be evaluated with adverse events reported for the period ranging from informed consent and during the study to the end of treatment visit including 56 days (8 weeks) after the last administration of the clinical study treatment.