Statement of problem: Many risk factors cause progression of peridontitis. Smoking is one of these factors and due to increasing rate of smokers, there is need to study more about the effect of smoking on periodontal indicators.Purpose: The aim of this study was clinical evaluation of smoking effects on periodontal tissues in referring patients to oral medicine and periodontics department in Tabriz dental faculty.Materials and method: This study was an analytical, cross-sectional study. Sample size consisted of one hundred patients with chronic periodontitis. Of these patients, 50 smoker patients (34 Heavy smokers and 16 Light smokers) entered into case group and 50 non-smoker patients entered into control group. After ensuring age matching between smokers and non-smokers, periodontal measurements such as clinical probing depth (CPD), gingival recession (GR), clinical attachment level (CAL), tooth mobility (TM) and bleeding on Probing (BOP) were obtained and recorded in special questionnaires. Data analysis was performed by SPSS soft ware and Tukey and Pearson tests.Results: Clinical probing depth, gingival recession, clinical attachment loss and tooth mobility increased significantly in Heavy smokers compared with non-smokers and Light smokers (p<0.05), while no statistically significant differences were found between non- smoker and light smoker groups.Considering bleeding on probing, there was declining trend in BOP in Heavy smokers compared with non-smokers and Light smokers (p=0.00). There was not significant differences upon the effect of cigarette consumption (based on pack years) in the mentioned indices (p>0.05) between the two groups.Conclusion: Based on the results of this study which showed an increasing rate of intensity in periodontal indicators in smokers group compared with non-smoker, specific programs to increase public awareness on the effect of smoking should be recommended.Key words: Periodontitis, Heavy smoker, Light smoker