Introduction: Vitamin D3 plays an important role in the mineralization mechanism and is often deficient in diabetic patients. The objective of this study was to investigate the odonto/osteogenic differentiation potential of the combination of mineral trioxide aggregate (MTA)/1 alpha,25-dihydroxyvitamin D3 (VD3) on dental pulp stem cells (DPSCs) of patients with type 1 diabetes mellitus (T1DM). Methods: DPSCs isolated from donors (control and T1DM) were cultured and characterized. Cell proliferation and wound healing assays were performed. DPSCs were exposed to 4 different media: growth medium (Dulbecco's modified Eagle's medium, 10% fetal bovine serum, antibiotic, and antimycotic), differentiation medium (DM) (growth medium plus u-glycerophosphate and ascorbic acid), DM + MTA (DM plus 0.02 mg/ mL MTA), and DM + MTA + VD3 (DM + MTA and 10 nmol/L vitamin D3). Odonto/osteogenic differentiation of DPSCs was evaluated by the alizarin red test, relative real-time polymerase chain reaction (dentin sialophosphoprotein, dentin matrix protein 1, collagen type 1 alpha 1, and osteocalcin), immunocytochemistry (antibone sialoprotein II, anti-dentin matrix protein 1, and anti-collagen type 1 alpha 1), and Western blot (dentin matrix protein 1 and osteocalcin) methods. Results: The proliferation rates of DPSCs isolated from controls were significantly higher than DPSCs isolated from T1 DM in a time-dependent manner (P < .05). Alizarin red staining and the expression of odonto/osteogenic markers showed that odonto/osteogenic differentiation was more pronounced in controls (P < .05) compared with T1DM patients. Although DM + MTA caused the odonto/osteogenic differentiation in DPSCs derived from controls, DM + MTA + VD3 resulted in the odonto/osteogenic differentiation in DPSCs of T1DM patients (P < .05). Conclusions: Odonto/osteogenic differentiation was affected by both supplements used for differentiation and the systemic disease, diabetes mellitus. The differentiation potential of T1DM-derived DPSCs was clearly increased with the VD3 supplement, although it was not as efficient as in the controls. The VD3 supplement showed a positive effect on the differentiation of T1DM DPSCs compared with MTA alone.