Background: Endothelial progenitor cells (EPCs) migrate to ischemic or injured sites to participate in angiogenesis, whereas periosteum-derived stem cells (PDSCs) can differentiate in multiple directions. This study aimed to investigate the roles and mechanisms of EPCs in promoting the osteogenic differentiation of PDSCs. Methods: Alizarin red and alkaline phosphatase staining was conducted after 3, 7, and 14 days of co-culture to evaluate the osteogenic differentiation of PDSCs. Subsequently, exosomes were isolated from EPCs. Following 7 and 14 days of treatment with PDSCs, scanning electron microscope and alizarin red staining were performed. EPCs with methyltransferase-like 3 (METTL3) knockdown and PDSCs overexpressing serum and glucocorticoid-induced kinase 1 (SGK1) were constructed to further explore the underlying mechanism. Results: As the co-culture time increased, the alkaline phosphatase and calcification levels gradually increased in the co-cultured group. EPC-derived exosomes also elevated alkaline phosphatase and calcification levels of PDSCs, and significantly upregulated osteopontin (OPN), osteoprotegerin (OPG), and runt-related transcription factor 2 (RUNX2) expression (p < 0.05). Both immunofluorescent staining and western blot revealed that treatment with the EPC-derived exosomes significantly enhanced the expression levels of METTL3 and SGK1 were significantly enhanced in PDSCs compared with those in control cells (p < 0.05). Exosomes were successfully isolated from EPCs with METTL3 knockdown; these exosomes significantly downregulated the expression levels of OPN, OPG, and RUNX2 (p < 0.05). SGK1 expression was significantly upregulated by EPC-derived exosomes in PDSCs overexpressing METTL3 (p < 0.05) and markedly downregulated in PDSCs treated with EPC-derived exosomes with METTL3 knockdown (p < 0.05). Conclusions: EPC-derived exosomes carrying METTL3 may promote the osteogenic differentiation of PDSCs by regulating SGK1.