Objective: The aim of this study is to measure melatonin levels in gingival crevicular fluid of subjects with clinically healthy periodontal tissues , and patients having chronic peridontitis , before and after non- surgical periodontal therapy. Materials and Methods: This study was conducted on 30 subjects divided into 15 individuals with clinically healthy periodontium and 15 patients suffering from chronic periodontitis (21 females and 9 males in age range 30-45). Patients were recalled in one month and two months after the treatment. 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 Melatonin in the GCF samples was determined using commercially available human-specific ELISA that were in accordance with the manufacturer’s instructions (total Melatonin ELISA kit). Results: In chronic periodontitis group treated by SRP, all clinical parameters showed statistically significant improvement after scaling and root planing, This improvement was accompanied by increase the mean concentration of Melatonin in GCF. 1. Conclusion: Melatonin was expressed in GCF and may be considered one of the markers of periodontal disease. 2. Levels of GCF melatonin decreased in chronic periodontitis compared to the healthy group, showing the protective nature of melatonin, which is mainly credited to its anti-inflammatory properties. 3. After the non-surgical periodontal therapy, chronic periodontitis patients were significantly improved the clinical parameters. This improvement was accompanied by increase the mean concentration of Melatonin in GCF. 4. Further research is required to standardize the amount of GCF melatonin