This clinical controlled study included 25 subjects, both groups were selected to be systemically free. No pregnant females or smokers were allowed to participate in this study. No patient were included if he/she had received any periodontal or antibiotics treatment during the last six months. The study group was divided into 2 groups: Group I ( chronic periodontitis group): consists of 15 patients with multiple sites with probing depth (PPD) ≥4 mm, clinical attachment loss (CAL) ≥ 4 mm and bleeding on gentle probing. Group II (control group): consisted of 10 healthy individuals. Control subjects had to meet the following criteria for inclusion: probing pocket depth PPD < 3mm, no clinical attachment loss, no bleeding on probing (BOP).All subjects were screened by comprehensive periodontal examination and full periodontal charts were obtained. The following clinical periodontal status in patients and healthy controls: gingival index (GI), plaque index (PI), probing pocket depth (PPD) and clinical attachment level (CAL). In both groups GCF samples were collected, in chronic periodontitis group at the initial visit, 6 weeks after treatment. IL-23 was measured in GCF using Enzyme linked immunosorbent assay (ELISA) technique.The results of the present study revealed significant positive correlation between IL-23 and all clinical parameters (before treatment) and also between IL-23, PPD and CAL (after treatment).