We investigated the association between estimated time from the onset of multiple sclerosis (MS) plaques and myelin- and axon-related quantitative MRI measurements using synthetic MRI (SyMRI) and neurite orientation dispersion and density imaging (NODDI). We retrospectively analyzed 32 MS patients with 73 newly appearing plaques. MS plaques with longer estimated time from the onset had significantly lower myelin volume fraction and higher g-ratio. It is suggested that myelin in plaques is under ongoing damage more than axons. SyMRI and NODDI may be useful for the quantitative assessment of temporal change in MS plaques.