Objective: To investigate the effect of osteoprotegerin (OPG) on the cementoblastic activity of a clonal population of immortalised murine cementoblasts (OCCM-30) in vitro. Methods: OCCM-30 cells were transiently transfected with the mouse OPG using the Avalanche transfection reagent. The ectopic expression of OPG was confirmed by enzyme-linked immunosorbent assay and quantitative polymerase chain reaction. The cell counting Kit-8 assay was used to investigate the effect of OPG on cell proliferation. The expression levels of cementoblastic-related mRNA and protein in the transfected OCCM-30 cells were detected using real-time PCR, Western blotting and immunohistochemical staining. Results: Satisfactory transfection efficiency was observed 48 h after transfection. The results of the cell proliferation assay indicated that the expansion rate of the OPG transfection group was greater than that of the control group at both 72 h and 96 h. The mRNA levels of osterix (Osx), protein kinase B (Akt1), cementum attachment protein (CAP) and osteopontin (Opn) were significantly upregulated (P 0.05) in the OPG group. Protein levels of OPN, bone sialoprotein II (BSP II), osteocalcin (OC) and CAP, which are responsible for osteogenetic and cementoblastic activity, were significantly increased in the OPG-overexpressing group. Conclusion: Overexpression of OPG in OCCM-30 cells promotes cementoblastic activity. Schlagwörter: cementoblastic, OCCM-30, osteoprotegerin (OPG), root repair, root resorption