Aim: 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: The results proved the benefit of Melatonin as a promising adjunctive therapy in improving periodontal parameters. However, further long-term studies with large sample size are needed..