Diabetes mellitus (DM) has reached pandemic prevalence, significantly impacting global health. Accumulating evidence has highlighted a bidirectional relationship between diabetes and depression, with blood-brain barrier (BBB) disruption playing a pivotal role in the pathogenesis of and therapeutic approaches to both disorders. Mesenchymal stem cells (MSCs) have emerged as a promising cell-based therapeutic strategy for DM; however, their potential to mitigate DM-associated emotional deficits remains unclear. This study investigates whether MSCs can restore BBB integrity and improve emotional deficits in a diabetic mouse model via matrix metalloprotein-9 (MMP-9) inhibition. We used biochemical, molecular, and behavioral analyses to assess BBB function, inflammation, and emotional behavior. Our results demonstrated that diabetic conditions induce BBB dysfunction, characterized by the MMP-9-mediated degradation of tight junction (TJ) proteins claudin-5 (Cldn5) and occludin (Ocln), alongside neuroinflammation and emotional impairments. Notably, MSC administration restored BBB integrity and attenuated neuroinflammation by suppressing MMP-9 activity and upregulating TJ proteins. Importantly, MSC treatment not only alleviated anxiety- and depressive-like behaviors but also enhanced glycemic control in DMmodels. These findings elucidate the mechanistic basis of MSC therapy for DM-related neuropsychiatric complications and, crucially, reveal its dual therapeutic efficacy in concurrently ameliorating both neuropsychiatric symptoms and metabolic dysfunction in DM models. This synergistic therapeutic effect provides a translational rationale for advancing MSC-based therapies into clinical applications.