Background and objectives: YKL–40 is an acute phase protein chiefly regulated by IL–6 and is expressed during the course of inflammation. Multiple cytokines have been identified in gingival tissues that causes tissue destruction associated with progressing periodontitis . In this context the present study was undertaken to quantify YKL–40 levels in chronic and aggressive periodontitis patients. Clinical parameters were compared and correlated. Material & Methods: Gingival tissue samples were obtained from three groups:– Healthy (n=30), chronic periodontitis (n=30) and aggressive periodontitis subjects (n=30) .The samples were quantitative analysed by ELISA. Results : YKL–40 levels significantly increased in chronic periodontitis as compared to aggressive periodontitis and healthy subjects.   Conclusion: YKL–40 protein has a role in the immunopathogenesis of periodontitis and can be used as an useful inflammatory biomarker in periodontal diseases.