Background <p>Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease (ESRD) globally, presenting a significant therapeutic challenge. Extracellular vesicles (EVs) from mesenchymal stem cells (MSCs) have emerged as promising therapeutic agents. This study explored the therapeutic effects and mechanisms of EVs derived from human placental mesenchymal stem cells (hP-MSCs) on DKD.</p> Methods <p>EVs were isolated from cultured hP-MSCs and administered to streptozotocin (STZ)-induced diabetic mice and high glucose–treated glomerular mesangial cells. The therapeutic impact of EVs was assessed through histological analysis and biochemical assays. miR-99b-5p expression in EVs and its role in modulating the mechanistic target of rapamycin (mTOR)/autophagy pathway were examined via western blotting and RT‒qPCR.</p> Results <p>Treatment with hP-MSC-derived EVs significantly alleviated renal fibrosis and improved renal function in DKD models. These EVs were enriched with miR-99b-5p, which targeted and inhibited mTOR signaling, thereby increasing autophagic activity and reducing cellular proliferation and extracellular matrix accumulation in renal tissues.</p> Conclusions <p>hP-MSC-derived EVs can mitigate renal injury in DKD by modulating the miR-99b-5p/mTOR/autophagy pathway. These findings suggest a potential cell-free therapeutic strategy for managing DKD.</p>