Purpose: To assess the patterns of myelodysplastic syndrome(MDS) and aplastic anemia(AA) on MRI of the spinalbone marrow and to find the differential points between the two groups. Materials and Methods: Fourteen patientswith MDS(n=7) and AA(n=7) were studied using magnetic resonance imaging. Sagittal images from the lower thoracicand lumbar vertebral marrow were evaluated on T1-weighted and STIR images. Five distinct patterns of signalintensity of the T1-weighted and STIR images were classified. T1 and T2 relaxation times and T1 marrow /fat signalintensity ratio were measured and analyzed (t-test). The cellularity of bone marrow was evaluated on histologicslides. Results: MDS showed homogeneously low signal intensity on T1WI and high signal intensity on STIR image,indicating hypercellular marrow, whereas AA showed relative high signal intensity on T1WI and low signal intensityon STIR image, representing fatty marrow. T1 and T2 relaxation time(T1 for MDS=750.26 msec 177.50, T1 for AA=413.21 msec 167.39 (p< 0.000), T2 for MDS=91.86 msec 14.16, T2 for AA=81.44 msec 15.31 (p< 0.001) and T1marrow/fat signal intensity ratio(0.22 0.048 in MDS, 0.30 0.083 in AA(p< 0.000)) revealed statisticallysignificant difference between the two groups. Conclusion: Although the marrow aspiration and needle biopsy aremandatory in hematologic disease for diagnosis, there is limited in assessing the change of total marrow mass.Therefore MRI of bone marrow might be useful in distinguishing MDS from AA because of its ability ofrepresentation of total marrow mass.