Bone mesenchymal stem cell (BMSC)-derived exosome (BMSC-Exo) could be a treatment method for ischemic injury. In ischemic cerebrovascular disease (IC), microglia is pivotal in neuronal damage and remodeling. This study explores the mechanisms of BMSC-Exo miR-148b-3p in regulating oxygen-glucose deprivation/reoxygenation (OGD/R)-induced human microglial clone 3 (HMC3) cell activation. Transmission electron microscopy (TEM) and qNano were used to assess BMSC-Exo features. The functions of BMSC-Exo miR-148 b-3p in OGD/R-induced HMC3 cell activation were explored via MTT assay, flow cytometry, scratch, transwell, and enzyme-linked immunosorbent assay (ELISA) assays. A dual-luciferase reporter assay was performed to determine the relationship between miR-148b-3p and Delta-like ligand 4(DDL4) or neurogenic locus notch homolog protein 1 (Notch1). OGD/R decreased miR-148b-3p expression in HMC3 cells. After BMSC-Exo treatment, miR-148b-3p expression was upregulated, cell viability and migration were inhibited, cell cycles remained in the G0/G1 phase, and proinflammatory cytokines were decreased in OGD/R-induced HMC3 cells. More importantly, BMSC-Exo miR-148b-3p could further strengthen BMSC-Exo effects. DDL4 and Notch1 are direct targets of miR-148b-3p, respectively. Moreover, the knockdown of DLL4 or Notch1 could inhibit OGD/R-induced HMC3 cell activation. BMSC-Exo miR-148b-3p inhibited OGD/R-induced HMC3 cell activation via inhibiting DLL4 and Notch1 expression, which provided a new strategy for treating cerebral ischemia.