Purpose: To analyze, in vitro, the influence of O2 pressure on the adhesion, proliferation, and osteogenic differentiation of human dental pulp stem cells (DPSC) on β-tricalcium phosphate (β-TCP) scaffold. Materials and Methods: DPSC, positive for the molecular markers CD133, Oct4, Nestin, Stro-1, and CD34, and negative for CD45, were isolated from extracted third molars. Experiments were started by seeding 200,000 cells on β-TCP cultured under 3% or 21% O2 pressure. No osteogenic medium was used. Eight different cultures were performed at each time point under each O2 pressure condition. Cell adhesion, proliferation, and differentiation over the biomaterial were evaluated at 7, 13, 18, and 23 days of culture. Cell adhesion was determined by light microscopy, proliferation by DNA quantification, and osteogenic differentiation by alkaline phosphatase (ALP) activity analysis. Results: DPSC adhered to β-TCP with both O2 conditions. Cell proliferation was found from day 7 of culture. Higher values were recorded at 3% O2 in each time point. Statistically significant differences were recorded at 23 days of culture (P = .033). ALP activity was not detectable at 7 days. There was, however, an increase in ALP activity over time in both groups. At 13, 18, and 23 days of culture, higher ALP activity was recorded under 3% O2 pressure. Statistical differences were found at day 23 (P = .014). Conclusion: DPSC display capacity of adhering to β-TCP under 3% or 21% O2 pressure conditions. Cell proliferation on β-TCP phosphate is significantly higher at 3% than at 21% O2 pressure, the most frequently used O2 tension. β-TCP can itself promote osteogenic differentiation of DPSC and is enhanced under 3% O2 compared with 21%. Keywords: bone regeneration, dental pulp stem cells, O2 pressure, tissue engineering, β-tricalcium phosphate