Abstract Context Bone marrow adiposity (BMAT) alterations in patients with type 2 diabetes mellitus (T2DM) may contribute to adverse bone effects. Objective Characterization of BMAT content and composition in patients with well-controlled T2DM. Design cross-sectional study with two groups of postmenopausal women: one with T2DM and the other without. Main outcome measures The proton density fat fraction (PDFF) of the lumbar spine and proximal femur, comprising the femoral head, neck, and diaphysis, was assessed using chemical shift-based water-fat separation imaging (WFI). MRI with spectroscopy (¹H-MRS) was performed in a subgroup of participants to confirm the PDFF measurements and determine the apparent lipid unsaturation level (aLUL) at the L3 vertebrae and femoral neck. The association of imaging-based PDFFs and aLUL between diabetes groups was investigated by adjusting for confounding factors using a linear mixed model. Results Among 199 participants, patients with T2DM (n = 29) were significantly heavier (p < 0.001) and had a higher BMD (p<0.001 for all sites) than non-diabetic patients (n = 170). When PDFFs were compared after adjusting for age, BMI, and BMD, the femoral head WFI-based PDFF was lower in patients with T2DM (mean (standard error) 88.0% (0.7) versus 90.6% (0.3), p < 0.001). Moreover, the aLUL at the L3 vertebrae was lower in patients with T2DM (n = 16) than in without (n = 97) (mean (standard error) 3.9% (0.1) versus 4.3% (0.1), p = 0.02). Conclusions The content and composition of BMAT are modified in postmenopausal women with T2DM and these changes occur at specific sites.