Objective: the objective of this study was designed to evaluate the effect of non-surgical periodontal therapy on glutathione levels in saliva and gingival crevicular fluid among diabetics with chronic periodontitis. Subjects and methods A total number of 60 patients were selected consists of three groups: group 1 was 20 patients with healthy periodontal condition, group 2 was 20 patients with chronic periodontitis and group 3 was 20 diabetic patients with chronic. Scaling, root planning and oral hygiene instructions were performed for patients in group 2 and group 3.Saliva and GCF samples were collected from each subjects at baseline (before treatment) , one month and three months after performing the non –surgical periodontal therapy .Results Following non-surgical therapy, glutathione levels in diabetic and chronic periodontitis groups improved significantly when compared to base line levels.No significant correlation between glutathione, age and disease activity in diabetic & periodontitis groups. Conclusion Glutathione levels should be considered a marker for disease and the concentration of reactive oxygen species in human body and an important indicator for the progression of the periodontal treatment in patients with periodontal disease.