Aim: Melatonin catch more attention as adjunctive periodontal therapy. This study was conducted to assess the benefit of locally delivered melatonin gel as adjunctive to scaling and root planning (SRP) in the treatment of chronic periodontitis Subjects and Methods: Forty chronic periodontitis selected patients ,divided into two groups. Group I: included 20 chronic periodontitis patients, treated by conventional periodontal therapy SRP combined with intra- pocket application of Melatonin gel once weekly for 1 month begin application at the second week after initial therapy. Group II: included 20 chronic periodontitis patients, treated by SRP combined with the injection of placebo, weekly for one month. The periodontal parameters were recorded at baseline, 1week, 1and 3 months .Gingival crevicular fluid (GCF) samples were collected and a quantitative measurement of receptor activator nuclear K ligand (RANKL) was carried out by using Enzyme-Linked Immunosorbent Assay (ELISA) at baseline, 1week, 1 and 3 months. Results: We found noticeable significant reduction in all clinical parameter and in the amount of GCF RANKL in group I in all evaluation period at 1 ,3-month over group II . Conclusion: We found noticeable significant reduction in all clinical parameter and in the amount of GCF RANKL in group I in all evaluation period at 1 ,3-month over group II .