The aim of this study was to determine whether exosomes from Nicotinamide phosphoribosyltransferase (NAMPT)-overexpressing mesenchymal stem cells (MSC NAMPT-Exo) can attenuate aortic stenosis (AS) and explored the underlying mechanism. NAMPT expression was examined in EC CXCR4 KO (AS) mouse hearts. Six-week-old AS mice received weekly injections of NAMPT-Exo, MSC-Exo, or PBS for three weeks, followed by echocardiography and histological examination of the valves (H&E, Alizarin Red, immunofluorescence). Cardiac ECs from control, AS, and NAMPT-Exo-treated mice were analyzed for miRNA expression (miR-146a-3p/5p, miR-125b-5p, miR-142a-5p). NAMPT expression was decreased in AS hearts. Treatment with NAMPT-Exo reduced aortic valve peak velocity, valvular thickening, and microcalcifications, while improving ejection fraction, fractional shortening, and ventricular dimensions. AS endothelial cells showed elevated levels of miR-146a-3p, miR-146a-5p, and miR-142a-5p, NAMPT-Exo specifically normalized miR-146a-3p. Histology revealed EndMT in AS valves, which was diminished by NAMPT-Exo. In vitro, inhibiting miR-146a-3p suppressed TGF-β-induced EndMT. Our results demonstrate that NAMPT-enriched MSC-derived exosomes effectively slow the progression of AS. Additionally, our findings highlight miR-146a-3p as a key regulator of EndMT, suggesting it as a potential molecular target for future therapies.