Multiple sclerosis (MS) is an immune-mediated demyelinating disorder of the central nervous system (CNS) that leads to neurodegeneration. Remyelination is an essential reparative process in MS. While remyelination occurs efficiently during the early stages of the disease, it significantly declines with disease progression. This is despite the presence of oligodendrocyte progenitor cells (OPCs) within the lesions with the ability to generate new myelinating oligodendrocytes (OLs). Understanding how OPC and OL are regulated in MS lesions is critical to promote remyelination in chronic MS lesions. Emerging studies indicate that a balanced activity of mTOR pathway is essential for normal differentiation and maturation of OLs. Other findings have suggested that the integrated stress response (ISR), which occurs upon phosphorylation of eIF2α, has a protective role in remyelination. In this study, we aimed to characterize the activity of mTOR and the ISR in OPCs and OLs during acute and chronic demyelination and remyelination by using a cuprizone mouse model of demyelination. We also used primary in vitro systems to assess the changes in OPC maturation under MS-like conditions. We found that mTOR and ISR activity is increased in OPCs and OLs during both acute and chronic demyelination in cuprizone mice, and this expression is sustained during the remyelination period. In vitro, we confirmed that rapamycin-inhibition of mTORC1 results in decreased OPC proliferation and differentiation and inhibit OL maturation and morphological complexity in vitro, while increasing their lysosomal activity. Treating OPCs with MS-relevant cytokines also decreases OPC proliferation acutely and reduces their differentiation while promoting lysosomal activity. This study provides initial data that suggest the involvement of mTOR and ISR in oligodendrocyte behavior in demyelinating lesions. Future studies are required to determine the role of these pathways in impaired remyelination during chronic MS.