Investigating optimal NODDI intrinsic diffusivity d|| values in the first years of life would provide accurate diffusion properties estimation. We aimed to investigate d|| for 1-36 months range. Diffusion data from 265 baby Human Connectome Project subjects were processed and used for NODDI model fitting with MDT tool. Among different d|| tested, optimal value was chosen according to maximum LogLikelihood maps and investigated as a function of age. Infants exhibit optimal d|| values of 1.95 µm2 ms-1, where d|| decreases for increasing age. Based on our results, 1.7 µm2 ms-1 represent a suboptimal assumption in the case of infant population.