Diffusion MRI has been regarded as an assessment in characterizing brain tissue integrity. However, the information of tissue heterogeneity is often overlooked. To investigate the feasibility of diffusional heterogeneity in gray matter through DKI derived diffusivities, six spontaneously-hypertensive rats (SHR) in different ages were scanned on a 7T small animal MR scanner. The differences of heterogeneity of diffusivities and kurtosis between different ages were revealed, which may imply its possibility for tissue characterization. Therefore, the diffusional heterogeneity could be suggested to be a potential image-based biomarker for evaluating tissue integrity.