Oral-resident bacteria cause various diseases in the oral cavity, and studies have been conducted to inhibit the activities of many of such bacteria. This study was conducted to investigate the antibacterial effect of the natural extract Forsythiae fructus against the oral-resident bacteria Streptococcus intermedius (S. intermedius) and Streptococcus gordonii (S. gordonii), characterized by antiinflammation and antimicrobial activity. The clearzone confirmation method was used to test the antimicrobial activity, and the number of colony-forming units (CFUs) was checked to measure the bacterial proliferation. For the experiment, 5, 10 and 20 mg/mL of Forsythiae fructus extract were set as the experimental groups, and the group without any treatment was set as the control group. For the results of the antimicrobial activity testing, the size of the clear zone became larger as the concentration increased from 5 to 10 and 20 mg/mL compared to the control group. As for the results of the CFU measurement, many bacteria were observed in the control group while no bacteria appeared in all the experimental groups. Therefore, the present study confirmed the antibacterial effect of Forsythiae fructus extract in the oral cavity, which could be used as basic data for the development of antimicrobial agents using natural extracts against oral-resident bacteria.