Objective: To compare the biological characteristics of dental pulp stem cells (DPSCs) and inflamed dental pulp derived stem cells (I-DPSCs) in vitro and their regeneration potential in Beagle immature premolars. Methods: Pulpitis was induced in the premolars of one beagle dog by opening the pulp chamber for 2 weeks, and inflammation was histologically confirmed. DPSCs and I-DPSCs were isolated from normal and inflamed dental pulp, and cell morphology, expression of mesenchymal stem cell markers, clone formation ability, cell proliferation and osteogenic/odontogenic differentiation potential were compared. The dental pulp of 20 roots from 10 immature premolars was extracted and divided into two groups. DPSCs or I-DPSCs with scaffolds were transplanted into the root canals. The roots were extracted after 3 months, and pulp regeneration was evaluated by histological analysis. The data were statistically analysed using one-way ANOVA and a Student t test. Results: Histological analyses showed lymphocyte infiltration and elevated TNF-α expression, which confirmed the diagnosis of pulpitis. I-DPSCs showed similar morphology, marker gene expression and clone formation ability but greater proliferation ability and osteogenic/odontogenic differentiation potential. Pulp-like tissue formation and bone- and dentine-like tissue deposition were observed in both DPSC- and I-DPSC–transplanted roots. Conclusion: DPSCs derived from inflammatory dental pulp tissue have similar biological characteristics to those from normal dental pulp and could mediate pulp and dentine regeneration in immature premolars. Keywords: dental pulp stem cells, inflamed dental pulp, tissue regeneration