Working memory is a critical cognitive functions affected after mild traumatic brain injury (MTBI). We investigate associations between white matter (WM) microstructure and working memory, using multi-shell diffusion MRI and WAIS-IV subtests. The significant positive correlations observed in normal controls (NC) between tissue microstructure markers (fractional anisotropy (FA) and axonal water fraction (AWF)) with letter-number sequencing (LNS) were not present in MTBI. For MTBI, a significant positive correlation was observed between axial kurtosis (AK) and digit span backward (DSB), not seen in NC. These results show clear differences in the relationship between WM microstructure and working memory performance after injury.