OBJECTIVE: Human periodontal ligament stem cells (hPDLSCs) attract attention for the periodontal regeneration therapy. Curcumin may promote osteogenic differentiation of hPDLSCs. This research aims to elucidate whether Curcumin displays promoting osteogenic differentiation and its mechanism. METHODS: The hPDLSCs were isolated from human periodontal ligament by immunomagnetic beads, identified with immumofluorescence. hPDLSCs were treated with 0, 5, 10, 20, 50, 100 μmol/L Curcumin. The early growth response gene 1 (EGR1) siRNA or plasmind were tranfected into the hPDLSCs. The viability, Alkaline Phosphatase (ALP) activity and mineralizaiton level of hPDLSCs were measured with 3-(4,5)-dimethylthiahiazo(-z-y1)-3,5-di-phenytetrazoliumromide (MTT) assay, ALP Assay Kit or Alizarin Red staining. The expression of EGR1, RUNX family transcription factor 2 (Runx2), bone gamma-carboxyglutamate protein (OC), secreted phosphoprotein 1 (OPN) and collagen type I alpha 1 chain (Collagen I), in hPDLSC were determined by Western blotting and quantitative reverse transcription-polymerase chain reaction. RESULTS: The isolated hPDLSCs were spindle or irregular, arranged in radial shape and shown positive expression of STRO-1, CD146 and Vimentin. Curcumin 10 μmol/L treatment maximal promoting the cells viability, ALP activities, mineralization, and levels of Runx2, OC, OPN, Collagen I and EGR-1 in hPDLSCs. EGR-1 siRNA transfection inversed Curcumin's promoting effect on ALP activities, mineralization, and levels of Runx2, OC, OPN, Collagen I and EGR-1 in hPDLSCs. While the EGR-1 plasmid transfection enhanced Curcumin's promoting effect on these parameters of hPDLSCs. CONCLUSION: Curcumin promotes the osteogenic differentiation of hPDLSCs, which may work through the EGR1. Curcumin may be a promising medicine for periodontitis treatment and periodontal regeneration.