Purpose: The effect of periodontal disease on blood cells and hematopoises mechanisms has been focused during recent years, and based on researches on this field, leukocyte and plate1ete production are changed by the periodontal disease which in turn is believed to be an etiologic factor for thromboembolic phenomenon and cardiovascular disease. Due to lack of information about the possible changes by periodontal disease and blood indices in our country, this study was done on the patients referred to the oral medicine and periodontic wards of Azad Islamic dental faculty during 1381-82.Material & Methods: This study was a historical cohort study. The patients with moderate to severe chronic periodontits (Bone loss & CAL > 3 at more than 30% sites) without systemic diseases and infection and history of using any drugs and/or antibiotics, surgery, recent trauma or tooth extraction selected as test group, meanwhile, among the patients referred to the oral medicine ward who were periodontally healthy (CAL < 1) samples were selected as control group. The interventional variables, (age, gender, education, smoking habit and remained teeth) were matched between two groups. After describing the procedure of research to all of the participants, consent forms were signed. Base line data, consisted of "CAL" and "PI" in the both groups were recorded. Samples of 2ml venous blood were collected in standard tubes containing EDTA, send immediately to the laboratory for analysis of blood cells with automatic cell counter (Sysmex K 1000).The smear blood sample was taken from each patient, and evaluated by pathologist, to determine differential counting of WBC.Results: The study was done on 60 participants (test=30, control=30). There was no significant difference between the test and control group in interventional variables. Laboratory tests showed significant differences in some of blood indices, leukocytes were elevated in periodontal patient compare to healthy controls (P<0.001). This finding was primarily explained by higher numbers of neutrophils in periodontitis (P<0.001). Periodontal patient had a higher number of platelet compared to control group (p<0.01). There were no significant differences in other indices. (RBC, HGB, MCV, MCH, MCHC) between two groups (P<0.05).Conclusion: This study showed that periodontal diseases due to its influence on hematopoises mechanisms and blood cell production may cause increased WBC count, neutrophil and platelets, without alteration on RBC, HOB and other blood indices.