The objective of this study was to compare the expression levels of interleukin (IL)-17 IL-17 and IL-23 in serum from patients with both oral lichen planus and chronic periodontitis (OLP-CP), patients only with oral lichen planus (OLP), patients only with chronic periodontitis (CP), and healthy controls (HC). The serum samples were collected from 35 OLP-CP patients, 35 OLP patients, 30 CP patients, and 30 healthy controls. ELISA test was used to detect expression levels of IL-17 and IL-23 in serum from these four groups. ELISA analysis showed significantly elevated levels of serum IL-17 in OLP-CP group compared with OLP group (P < 0.05) and HC group (P < 0.01). Serum IL-23 result showed that there was an increased expression level in OLP-CP compared with HC group (P < 0.01). Additionally, female OLP-CP group showed elevated level of serum IL-17 compared with female OLP group, and also erosive OLP-CP group demonstrated increased serum IL-17 level compared with erosive OLP group. Moreover, analysis showed positive significant correlations of serum IL-17 level with probing depth (P < 0.05) and plaque index (P < 0.05) in erosive OLP-CP patients. This study indicates that OLP-CP patients get higher expression level of serum IL-17 and had susceptibility to erosive or female subtype, which indicated that IL-17 may participate in the disease immunopathogenesis of both common oral diseases.