The antimicrobial effect of mastic gum, an ancient remedy for oral malodor, against Porphyromonas gingivalis, a known odorogenic periopathogenic oral bacterium, was tested using the agar diffusion test. Paper discs impregnated with mastic gum methanolic extract (MME) [0.5-4% (wt/vol)] produced inhibition zones of 10.5-13.7 mm, respectively, without showing signs of hemolysis, whereas chlorhexidine (0.2%)-impregnated discs, which showed greater inhibition (33.5 mm), also produced large and distinctive hemolytic zones (17 mm). Further analysis of the antimicrobial traits of MME revealed a logarithmic ratio between inhibition zone diameter and MME concentration (r = .99), indicating limited water solubility of this material. These results suggest that mastic gum may be used as a potential nontoxic local agent in treating oral malodor and gum disease.