Soluble forms of amyloid-β (Aβ) peptide have been proposed as candidates to induce oligodendrocyte (OL) and myelin dysfunctions in the early stages of Alzheimer's disease (AD) pathology. Nevertheless, little is known about how Aβ affects OL differentiation and myelination in vivo, and the underlying molecular mechanisms. In this study, we explored the effects of a brain intraventricular injection of Aβ on OLs and myelin in the developing spinal cord of zebrafish larvae. Using quantitative fluorescent in situ RNA hybridization assays, we demonstrated that Aβ altered myrf and mbp mRNA levels and the regional distribution of mbp during larval development, suggesting an early differentiation of OLs. Through live imaging of Tg(myrf:mScarlet) and Tg(mbpa:tagRFP) zebrafish lines, both crossed with Tg(olig2:EGFP), we found that Aβ increased the number of myrf