Cortical mean kurtosis (MK) of diffusion MRI characterizes microstructural complexity in the cerebral cortex. In this study, we tested a linear model that soma and neurite densities jointly contributed to MK with different weights. The actual soma and neurite densities were quantified from digitization of macaque brain histological images of Nissl and neurofilament staining. DKI was acquired from 6 postmortem macaque brains. We found actual MK measurement was accurately predicted by a weighted linear combination of soma and neurite densities from histological images with higher neurite density weight.