The purpose of this study is to investigate the effect of melatonin supplement along with non-surgical periodontal therapy on periodontal status, salivary melatonin, glycemic control, inflammatory markers and blood lipid profile in type 2 diabetic patients with chronic periodontitis. In this double-blind, single center clinical trial 46 diabetic patients with chronic periodontitis are selected and randomly divided into two intervention (n=23) and control (n=23) groups. Randomization will be done using sealed envelope method. The intervention group will receive two 3 mg Melatonin tablets per day, one hour before bedtime, for 60 days. The control group will receive two 3 mg placebo tablets (containing cellulose, silicon dioxide and starch) one hour before bedtime, for 60 days. Non-surgical periodontal therapy will be performed for all patients during this study. Some demographic data including age; sex; anthropometric indices such as weight, height, BMI, waist and hip circumference; biochemical indices including fasting blood glucose, HbA1C, lipid factors, inflammatory markers (IL-6 and hs-CRP), salivary melatonin; periodontal indices (bleeding index, pocket depth, plaque index and clinical attachment level), physical activity and 3-day 24-hour recall are evaluated pre and post intervention.