Periodontal diseases are the most common inflammatory disease worldwide which caused by the pathogenic organism living in biofilm. Aggregatibacter Actinomycetemcomitans (Aa) is the main player of the periodontitis disease pathology. Although some of the virulence factors of Aa has been identified up to now, its cytotoxic mechanism has not been clearly known yet. Although known virulence factors of Aa; ltx and cdt has been knocked out, the mutant Aa strains have retained the ability to induce apoptosis. Depending on the literature there must be another important virulence factor. 64kDa GroEL protein which is a molecular chaperone and a heat shock protein can be the potential candidate for being a virulence factor. AaGroEL protein has not been studied in terms of apoptosis up to now and it is not known how AaGroEL mediate immune regulation of T cells. In this study AaGroEL protein has been purified by using ATP Affinity chromatography and electroelution methods. After the purification step lps contamination has been removed by detoxi-gel endotoxin removal gel and detected by LAL Assay. Peripheral Blood Mononuclear Cells (PBMCs) were isolated by Ficoll Hypaque Density Gradient Centrifugation method. It was found that AaGroEL protein induces T cell apoptosis in dose and a time dependent manner. AaGroEL protein mediated T cell apoptosis has been detected by plasma membrane changes, activation of caspase-3 and DNA fragmentation. In conclusion, AaGroEL has antigenic properties that effect T lymphocytes by regulating immune response that would play important role in periodontal pathology.