Abstract: Objective: To investigate the expression level of serum periodontal ligament-associated protein-1(PLAP-1) in patients with chronic periodontitis(CP) and its relationship with the degrees of lesions and inflammation. Methods: A total of 142 CP patients were set as the CP group,and 112 healthy people during the same period were selected as the control group.According to the periodontal pocket depth(PD) and attachment loss(AL),the CP patients were divided into the mild group(48 cases),moderate group(50 cases) and severe group(44 cases).The expression level of PLAP-1 in serum was detected by qRT-PCR;the contents of interleukin-6(IL-6),interleukin-35(IL-35) and tumor necrosis factor α(TNF-α) were determined by enzyme-linked immunosorbent assay,and Pearson correlation was used to analyze the correlation between serum PLAP-1 expression and inflammatory factors,PD,AL and PLI. Results: The levels of PD,AL and PLI in the CP group were obviously higher than those in control group(P<0.01).Compared with the control group,the expression level of serum PLAP-1,IL-6,IL-35,TNF-α in CP patients obviously increased(P<0.01).The expression level of serum PLAP-1,IL-6,IL-35,TNF-α in the severe group was obviously higher than that in moderate and mild group(P<0.05),and the serum levels of PLAP-1,IL-6,IL-35 and TNF-α in the moderate CP group were higher than those in mild group(P<0.05).The results of Pearson correlation analysis showed that the expression level of serum PLAP-1 in CP patients was positively correlated with the levels of PD,AL,PLI,IL-6,IL-35 and TNF-α(P<0.05 to P<0.01). Conclusions: PLAP-1 is obviously highly expressed in the serum of CP patients,and closely related to the degree of lesions and inflammation.