Objective: To investigate the effect of overexpression of Notch intracellular domain (NICD) on proliferation and osteogenic differentiation of human periodontal ligament stem cells (hPDLSC). Methods: The third generation hPDLSC with stable overexpressing of NICD were assigned as experimental group, normal hPDLSC were as negative control group and hPDLSC transfected with empty vector were as blank control group. The effect of overexpressing NICD on proliferation ability of hPDLSC was detected by using cell counting kit-8 (CCK-8). Alizarin Red staining and real-time quantitative PCR (qPCR) were used to detect the effects of NICD on cementum attachment proteins (CAP), osteocalcin (OCN), Runt-related transcription factor 2 (RUNX2) and Notch signal pathway receptor Notch1. The effect of overexpressing NICD on hPDLSC osteogenic protein RUNX2 and flag marker protein (used to label NICD) were detected by using Western blotting. Results: CCK-8 results showed that there were no significant differences in A values amongst the three groups for 1-2 days (P>0.05). The number of cells in the experimental group was significantly increase than that of the two control groups from the third to seventh days (A values were 0.203±0.016, 0.364±0.014, 0.449±0.020, 0.549±0.020 and 0.570±0.020, respectively) (P<0.05). Alizarin red staining showed that compared with the blank control group and negative control group, the mineralized nodules in the experimental group had smaller formation range and lighter color, and the differences were statistically significant (P<0.05). The expressions of CAP gene (0.751±0.058, 0.887±0.025), osteocalcin gene (0.592±0.051, 0.670±0.045) and RUNX2 gene (0.319±0.038, 0.684±0.055) at 14 and 21 days in the experimental group were significantly lower than those in the negative control group respectively (P<0.05). However, the expression levels of Notch1 gene at 14 and 21 days (2.507±0.047, 4.041±0.219) were significantly higher than those of negative and blank control groups (P<0.05). The results of Western blotting showed that the expressions of flag marker protein (0.167±0.007, 0.204±0.010) at 14 and 21 days in the experimental group were significantly higher than those in the negative and blank control groups (P<0.05). However, the expressions of RUNX2 protein (0.075±0.006, 0.074±0.013) at 14 and 21 days were significantly lower than that in the negative control group (0.092±0.003, 0.118±0.008) and blank control group (0.174±0.006, 0.212±0.008) (P<0.05). Conclusions Overexpression of NICD can promote the proliferation capacity of hPDLSC and inhibit its osteogenic differentiation.