The current oral health status of people worldwide is alarming and different preventive measures have been initiated to address and fight this problem. To optimize the use of plants in pharmaceutical products and address microbial problems on oral health, this research tested the activity of a plant essential oil in a new formulation. The essential oil was extracted from the roots of Moras or Vetiver (Vetiveria zizanioides) plant and was formulated into a mouthwash. It was tested for its antiseptic activity in controlling the growth of microorganisms normally present in the mouth that possibly cause halitosis, dental caries and tooth decay. The test was conducted using the Plate Count Method wherein the source of the microorganisms is from the mouth swabs of three (3) healthy individuals. The mouth swabs were diluted and treated with the different controls in 1:5 ratios respectively. Listerine® was used as the positive control while alcohol and formulated mouthwash without vetiver oil (mouthwash 2) were used as negative controls. The vetiver essential oil and the formulated mouthwash with vetiver oil (mouthwash 1) were used as the treatments. The results showed that the essential oil and the formulated mouthwash with oil have more bacteriostatic activity against the microorganisms in the mouth as seen in the difference in the number of colonies before and after treatment. The oil alone has better activity than the formulated mouthwash and Listerine®. The study shows the presence of acceptable antiseptic activity by preliminary testing of the formulated mouthwash from the essential oil of Vetiveria zizanioides roots. The researchers recommend further studies about this plant oil especially on its specific constituents that render its antiseptic property, sensitivity testing of the formulated mouthwash, further tests for antiseptic effectivity of the oil and formulated mouthwash, and other phamacologic uses as well as other formulations of the plant oil.