Many studies proved the Prevelance of (HSV ) Herpes Simplex Viruses and its involvement in occurrence of the periodontal disease and its progression .Recent studies prove effects of HSV viral load on disease severity and rate of progression in periodontitis. This study aimed to compare the prevalence and load of Herpes simplex virus 1 (HSV -1), Epstein-Barr Virus (EBV) and Human Cytomegalovirus (HCMV) in Sub gingival plaque samples and its effect on severity in chronic periodontitis and aggressive periodontitis. A total of 60 samples from the systematically healthy patients with chronic periodontitis n=30 (mean age, 35 ± 7). And n=30 aggressive periodontitis participated in this study Clinical periodontal evaluation included the plaque index (PI) (Loe and Silness), bleeding on probing (BOP) (O’Leary), bleeding index, periodontal pocket depth (PPD) and Clinical Attachment Level Measurement. Plaque sample taken from > 6 mm periodontal pockets and from ≥ ≥ ≥ ≥ ≥ 3 mm sulcus depth in a quadrant of the same patient using periodontal curettes in chronic periodontitis and plaque samples taken from periodontal pockets in aggressive periodontitis with CAL >6mm. A Taq-man Real-Time Polymerase Chain Reaction assay was used to identify genomic copies of periodontal HSV-1, HCMV and EBV. Data were analyzed by the Wilcoxon-signed ranks and Friedman tests using the SPSS 16 software. Out of 60 samples of subgingival plaque samples taken from the patients with chronic periodontitis and aggressive periodontitis. HSV count was least in the tissue sample with PD < 3 mm to 5mm (P < 0.05) in moderate chronic periodontitis sites. The highest HSV count was in samples with PD > 6 mm (P < 0.05). in severe chronic periodontitis sites and aggressive periodontitis sites. According to the results of this study, quantification OF HSV 1 HCMV and EBV observed in this study is high in plaque samples of aggressive periodontitis and severe chronic periodontitis sites compared with moderate chronic periodontitis sites.