There have been several magnetic resonance (MR) imaging biomarkers of Alzheimer’s disease (AD) for early diagnosis. Cortical mean diffusivity (MD) is one of them for the study of the cortical microstructural change in AD. However, the feasibility of MD often remains in doubt as partial volume effects may overestimate the results. This study aims to investigate feasible gray matter microstructural biomarker with higher sensitivity for early AD detection. We propose diffusion tensor imaging (DTI) measure, ‘radiality’, for early AD biomarker. It is a dot product between cortical surface normal vector and primary diffusion direction, which reflects the fiber orientation within the cortical column. Here, we gathered neuroimages from the Alzheimer’s Disease Neuroimaging Initiative (ADNI) database: 78 cognitive normal, 50 early mild cognitive impairment (EMCI), 34 late mild cognitive impairment (LMCI), and 39 AD patients. Then, we evaluated cortical thickness (CTh), MD, amount of amyloid and tau accumulations using positron emission tomography (PET), which are conventional AD biomarkers. Radiality was projected on gray matter surface to compare and validate the changes along other neuroimage biomarkers. Results showed decreased radiality primarily in entorhinal, insula, frontal and temporal cortex as disease progresses onward. Especially, radiality could delineate the difference between cognitive normal and EMCI group while other biomarkers could not. We looked into the relationship between the radiality and other biomarkers to validate its pathological evidence in AD. Overall, radiality showed high association with conventional biomarkers. Additional ROI analysis exhibits dynamics of AD related changes as stages onward. In conclusion, radiality in cortical gray matter showed AD specific changes and relevance with other conventional AD biomarkers with higher sensitivity. Besides, it could show group differences in early AD changes from EMCI which show advantage for early diagnosis than using conventional biomarkers. We provide the evidence of structure changes with cognitive impairment and suggest radiality as a sensitive biomarker for early AD.