Matrix metalloproteinase(MMP)-9 is considered important in tissue destruction in periodontitis. The aim of this study was to investigate the influence of smoking on MMP-9 in the gingival crevicular fluid(GCF). GCF samples in upper incisors area from 332 male subjects were collected after the informed consent. The dental examination included the assessment of oral hygiene, gingival inflammation and probing pocket depth. A quantitative assessment of MMP-9 levels in GCF was performed utilizing and immunological procedure. The mean MMP-9 concentrations found in GCF of smokers(30.86 ng/ml) and quit-smokers(29.82 ng/ml) differed from non-smokers(11.33 ng/ml), adjusted by age, gingival index and Community periodontal index(p<0.001). Smoking seems to influence MMP-9 in GCF regardless of gingival inflammation and age. It means smoking can destruct the periodontal tissue for itself.