Objective: IL-18 is a pro-inflammatory and tumor-suppressive cytokine. The purpose of the present study was to assess the level of interleukin- 18 (IL-18) in samples of gingival crevicular fluid (GCF) from chronic periodontitis patients before and after non-surgical treatment and to compare it with healthy controls.Materials and Methods: This study was conducted on 30 subjects divided into 15 individuals with healthy periodontium and 15 patients suffering from chronic periodontitis, where the level of IL-18 has measured before and after non-surgical therapy, with 2 weeks and 2 months follow up. Clinical recordings (GI, PI, PD, CAL) were scored for each participant in the study before and after treatment. GCF samples were obtained from each patient included in the present study and The amount of IL-18 in the GCF samples was determined using commercially available human-specific ELISA that were in accordance with the manufacturer’s instructions (total IL-18 ELISA kit). Results: In chronic periodontitis group all clinical parameters (GI, PI, PD, CAL) showed statistical significant improvement after scaling and root planing. There was a statistically significant decrease in mean IL-18 level after 2 weeks, then from 2 weeks to 2 months and again after 2 months.Conclusion: IL-18 in GCF can be considered a marker for disease and an important indicator for the progression of the periodontal treatment in patients with periodontal disease.