Periodontitis is an inflammatory disease of the supporting tissues of the teeth caused by specific microbes, resulting in progressive destruction of the periodontal ligament and alveolar bone in the oral cavity. The ABO blood groups in determining the susceptibility to various diseases have long been a subject of debate and periodontitis is one among them. Till date very few studies have been conducted to determine the association between ABO blood group and severity ofperiodontitis The aim of the study was to evaluate and Compare the association between ABO blood Groups and severity of Chronic Periodontitis. On oral examination, plaque index, gingival index, pocket probing depth, clinical attachment loss and the number of missing teeth were recorded. The blood group investigation was carried out by slide agglutination method.Analytical statistics were done. The Kolmogorov-Smirnov test was used for testing normality of data. The non-parametric Kruskal-Wallis test was used to check differences between the groups.66 Post hoc comparisons were done using Dunn-Bonferroni test.67 The chi-square test was used to check differences in proportions between groups. Software: SPSS (Statistical Package for Social Sciences) Version 20.1(Chicago, USA Inc.) There was a significant association of blood group ‘B’ with mild and moderate periodontitis and of blood group ‘ O’ with severe periodontitis (p =0.024).