Mapping tissue magnetic properties with MRI may improve the diagnosis of diseases and enhance our understanding of their basic mechanisms. However, MRI signals are sensitive to both structure and magnetic susceptibility, the so-called “magnetic microstructure”, rendering accurate susceptibility estimation a great challenge. Here, we present an analytical expression for the Larmor frequency of a white matter model of myelinated axons with axially symmetric microscopic susceptibility anisotropy and orientation dispersion. The modelled axons are surrounded by microscopic spherical inclusions with a scalar susceptibility. This goes beyond previous models of white matter magnetic microstructure.