Objective:To study the impact of smoking on C-reactive protein(CRP)concentration in gingival crevicular fluid(GCF) before and after initial treatment.Methods:18 smokers and 18 non-smokers with moderate or severe periodontal disease were recrui-ted into this study.The clinical indexes of periodontal examination of the patients were recorded,GCF samples of the patients were collected,CRP level in the samples was measured by radioimmunoassay balance method before and 4 weeks after initial treatment. Results:4 weeks after initial treatment,the clinical indexes and CRP concentration in GCF of the smoking group and non-smoking group were significantly lower than those before treatment(P <0.05),the changes of the smoking group were less than those of the non-smoking group(P <0.05).Conclusion:Smoking is an unfavorable factor of the initial periodontal therapy.