Abstract: Objective: To observe the effect of Porphyromonas gingivalis ATCC 33277 (P.g ATCC 33277) infection on human trophoblast cell line (HTR-8 cells) proliferation and apoptosis in vitro. Methods: HTR-8 cells were infected with P.g at a multiplicity of infection (MOI). Non-infected HTR-8 cells were used as the control. After Infection, the Cell Counting Kit(cck-8)was employed to assay the proliferation of HTR-8 cells. The apoptosis of HTR-8 cells were detected by mitochondrial membrane potential assay kit with JC-1 apoptosis detection kit. Result: At an MOI of 10, no inhibition on HTR-8 cells proliferation was observed following 24-72 h of P.g infection in contrast to the non-infected control (P>0.05). However, P.g significantly inhibited the proliferation of HTR-8 cells at an MOI of 100 or 200 at 24 h (P<0.01). In addition, cells infected with P.g at an MOI of 200 had a significantly lower lever of proliferation than cells infected with P.g at an MOI of 100 at 48 h (P<0.05) and 72 h (P<0.01). Furthermore, following 24 h of infection, P.g at an MOI of 200 significantly increased the rate of apoptosis in HTR-8 cells (P<0.01). A significant higher apoptosis rate in HTR-8 cells was also observed at an MOI of 100 after 48 h of infection (P<0.01). The rate of apoptosis was comparable between the control cells and the infected cells at an MOI of 10 at 24 h or 48 h (P>0.05). Conclusion: Our results demonstrate in vitro that P.g ATCC 33277 infection is able to suppress the proliferation of HTR-8 cells, and in the meantime, enhance the apoptosis of the cells. These results suggest that P.g-induced proliferation and apoptosis imbalance of trophoblast cells is involved in periodontal infection-associated preterm low birth weight.