INTRODUCTION: Pulp-capping procedures are routinely performed. The control of infection and biocompatibility of the pulp-capping materials are important factors in determining the treatment outcome. Calcium hydroxide has been considered the gold standard for this procedure. However, previous reports have reported the causes of failures with the use of calcium hydroxide. Mineral trioxide aggregate (MTA) has proved to be effective in the process of pulp capping. METHODS: Human dental pulp stromal cells (DPSCs) were cultured on gray MTA, and the levels of gene expression, secretion of vascular endothelial growth factor, and the surface morphology were analyzed. RESULTS: MTA promoted cell survival and proliferation, which was significantly different from the controls in human DPSCs. MTA up-regulated the expression of transcription factors like Runx2 and genes like osteocalcin, alkaline phosphatase, and dentin sialoprotein, which are important odontoblastic genes, thereby showing the ability to promote differentiation of the pulpal cells into odontoblast-like cells, which, in turn, are responsible for dentin bridge formation. MTA approximately induced a 1.7-fold increase in the secretion of angiogenic factors like vascular endothelial growth factor, which is important in the process of tissue healing and regeneration. The differences between the control and the MTA groups were statistically significant. Scanning electron microscopic studies revealed the differences in the surface morphologies between the control and the MTA groups. CONCLUSION: Overall, this study supports the biocompatible nature of MTA and the possible mechanism of dentin bridge formation along with tissue repair, all of which contribute to a successful treatment outcome.