Objective:To observe the effects of sonicated extract of Porphyromonas endodontalis(P.endodontalis)on the cell cy-cle and apoptosis of human osteoblastic hFOB 1 .1 9 cells.Methods:hFOB 1 .1 9 cells were treated with sonicated extract of P.end-odontalis at 0 (the control),1 ,1 0 and 1 00 μg/ml for 1 2,24 and 48 h respectively.MTT assay was used to examine cell prolifera-tion.The cell cycle distribution and apoptosis were examined by flow cytometry.Results:The sonicated exact of P.endodontalis in-hibited the proliferation of hFOB 1 .1 9 cells in a time-and dose-dependent manner.24 h treatment of 1 0 μg/ml and 1 00 μg/ml ex-act arrested the cell cycle of the cells in G1 phase,48 h treatment induced apoptosis in a dose-dependent manner.Conclusion:Sonicated exact of P.endodontalis may arrest hFOB 1 .1 9 cells in G1 phase and induce cell apoptosis,leading to inhibition of the cell proliferation.