The aim of this study is to test the antibacterial activity of the aqua extract of Phytolacca dodecandra roots against Bacillus cereus, Staphylococcus epidermidis, Streptococcus pyogenes, Escherichia coli, Serratia marcescens, Serratia liquefaciens, Salmonella typhi and Enterobacter aerogenes. The agar well diffusion method was used to determine the zones of inhibition by the extract, penicillin antibiotic (positive control) and sterile distilled water (negative control) against the organisms. The extract showed the highest activity against Enterobacter aerogenes (16.333+0.882 mm), followed by Bacillus cereus (14.33±0.333 mm), Escherichia coli (14.00±0.000 mm), Streptococcus pyogenes (13.00±0.000 mm). The zone of inhibition against Serratia marcescens was 7.33±0.333 mm, considered inactive because it is less than 8 mm. All the other organisms were not inhibited by the extract. The Tukey’s significant difference test showed significant differences with most of the pair-wise comparisons while a few zones were not significantly different from the other. The results from this study have shown that the aqua extract of P. dodecandra roots can inhibit both gram negative and gram positive bacteria in vitro. The pharmacologic mechanisms of action of the active ingredients must be studied and the active components can be considered for possible incorporation into conventional antibacterial drug production.