Aim: This study evaluates the effect of subgingival application of ozonated olive oil gel as an adjunct to scaling and root planning(SRP) in moderate chronic periodontitis . Subjects and methods: Thirty participants were involved in this study. fifteen  subjects with moderate chronic periodontitis as study cases, and other  fifteen healthy  subjects were introduced in the study as a negative control group. a split mouth randomized clinical study was conducted in 15 patients with moderate chronic periodontitis receiving scaling and root planning alone in  randomly selected quadrents and scaling and root planning associated with subgingival application of ozonated olive oil  gel in the other  quadrants. Periodontal  Clinical parameters  , plaque sample were performed at baseline, 1 month for all patients while the panoramic radiograph was taken for chronic periodontitis patients only.  Plaque Samples were cultured anaerobically  for detection of p.gingivalis and p.intermedia Results: scaling and root planning combined with Ozonated olive oil gel showed no  advantages in improving the clinical parameters except for Plaque index  , no effect on alveolar bone level  but it showed more favorable results microbiologically . Conclusion: Hence, adjunctive application of ozonated olive oil gel represents a promising natural product