The naked mole rat (NMR) is the longest-lived rodent, resistant to multiple age-related diseases including neurodegeneration. However, the mechanisms underlying the NMR’s resistance to neurodegenerative diseases remain elusive. Here, we isolated oligodendrocyte progenitor cells (OPCs) from NMRs and compared their transcriptome with that of other mammals. Extracellular matrix (ECM) genes best distinguish OPCs of long- and short-lived species. Notably, expression levels of CD44, an ECM-binding protein that has been suggested to contribute to NMR longevity by mediating the effect of hyaluronan (HA), are not only high in OPCs of long-lived species but also positively correlate with longevity in multiple cell types/tissues. We found that CD44 localizes to the endoplasmic reticulum (ER) and enhances basal ATF6 activity. CD44 modifies proteome and membrane properties of the ER and enhances ER stress resistance in a manner dependent on unfolded protein response regulators without the requirement of HA. HA-independent role of CD44 in proteostasis regulation may contribute to mammalian longevity. Display omitted •CD44 levels correlate with species maximum lifespan in OPCs, liver, skin, and fibroblasts•CD44 enhances basal ATF6 activity and ER stress resistance without the requirement of HA•CD44 localizes to the ER and alters ER proteome and ER membrane properties•CD44-dependent ER stress resistance is mediated by non-canonical activation of ATF6 Through comparative transcriptomics of short- and long-lived mammals, Takasugi et al. identified a correlation between longevity and CD44 levels. CD44 localizes to the ER and enhances basal ATF6 activity and ER stress resistance without HA. This HA-independent role of CD44 in proteostasis regulation may contribute to mammalian longevity.