Endoplasmic reticulum stress (ERS) occurred in S63del mutant CMT1B mice model, and few drugs has been studied. Mesencephalic astrocyte-derived neurotrophic factor (MANF) can inhibit ERS. This study aimed at investigating the effect of MANF on ERS of RT4-D6P2T schwannoma cells with S63del MPZ Mutation. Experimental grouping: blank control group, blank control + MANF group, lentivirus group, lentivirus + MANF group, S63del MPZ group, S63del MPZ + MANF group. CCK8 and Annexin-FITC/PI were used to detect cell proliferation and apoptosis. JC-1 was used to detect ΔΨm. MANF, GRP78 and CHOP mRNA and protein were detected by using RT-qPCR, western blotting and immunofluorescence. ER-Tracker and mito-tracker were used to observe the morphology of endoplasmic reticulum (ER) and mitochondria. Cell proliferation decreased (p < 0.001) and apoptosis increased (p < 0.001) in S63del MPZ group; cell proliferation increased (p = 0.005) and apoptosis decreased (p < 0.001) in S63del MPZ + MANF group. ΔΨm decreased (p < 0.001), MANF, GRP78, CHOP, ATF6, P-PERK/PERK, P-IRE1/IRE1, Bax and Caspase3 increased (p < 0.001) and Bcl2 decreased (p < 0.001) in S63del MPZ group. MANF, GRP78, CHOP, ATF6, P-PERK/PERK, P-IRE1/IRE1, Bax and Caspase3 decreased (p < 0.001) and Bcl2 increased (p < 0.001) in S63del MPZ group. ERS occurred in RT4-D6P2T cells with S63del MPZ mutation, and MANF exerted protective effect in RT4-D6P2T cells with S63del MPZ mutation.