Some infectious oral diseases are treated by medicinal plants in tropical areas, because they are abundant and cheap. The present work aimed to evaluate the antiseptic activity of the aqueous extract of Alchornea cordifolia leaves against three oral bacteria recognised as opportunistic pathogens, namely Streptococcus mitis, Staphylococcus epidermidis, and Micrococcus luteus. Fresh leaves of A. cordifolia were harvested, dried and pulverised. The extraction was performed by decocting in distilled water. The phytochemical screening was performed on the extract based on principles of colour change, and precipitation. Biological studies consisted in the in vitro antiseptic evaluation of the aqueous extract using the agar disc diffusion method, in comparison with a reference antiseptic mouthwash containing chlorhexidine. The extract had a 11.96% yield. The phytochemical screening revealed the presence of alkaloids, phenols, flavonoids, terpenes, tannins, glycosides, coumarins and saponins. The evaluation of the antiseptic activity revealed that the extract is active against S. mitis and S. epidermidis, and inactive against M. luteus. The diameters of inhibition zones were 16.9±1.1mm and 11.2±0.7mm at the concentration of 40mg/ml, and 7.7±0.3mm and 8.5±0.5mm at the concentration of 20mg/ml against S. mitis and S. epidermidis, respectively. Chlorhexidine did not inhibit S. mitis and showed diameters of inhibition of 13.0±1.0mm and 15.1±1.0mm against S. epidermidis and M. luteus, respectively. The minimal inhibitory concentration of the extract against the 2 sensitive bacteria was 20mg/ml.