Relaxation nuclear magnetic resonance imaging (R-NMRI) was employed to investigate the effects of thermooxidative aging in a hydroxy-terminated polybutadiene (HTPB)-based elastomer. A series of three-dimensional (3D) Hahn-echo-weighted single-point images (SPI) of the elastomer were utilized to generate a 3D parameter map of the aged material. NMR spin-spin relaxation times (T-2) were measured for each voxel producing a 3D NMR parameter (T-2) map of the aged polymer. These T-2 maps reveal a dramatic reduction of local polymer mobility near the aging surface with the degree of T-2 heterogeneity varying as a function of aging. Using correlations between NMR T-2 and material modulus, the impact of this heterogeneous thermooxidative aging on the material properties is discussed.