Objectives: CloSYSII® is a novel antibacterial rinse that has a stabilized chlorine dioxide formulation. The purpose of this study was to compare the bactericidal activity of this rinse with other oral rinses against 17 species of bacteria. Methods: Seventeen bacterial species commonly associated with oral health or disease were chosen for these studies and consisted of gram-positive, gram-negative, aerobic, and anaerobic bacteria. Rinses used in these comparative studies were Listerine®, Crest Pro-Health®, and Breath X®. Positive control was Peridex® and the negative control was Butterfield's buffer. For each organism, suspensions were prepared at standardized initial assay concentrations of 107 cfu/ml. Suspensions were added to undiluted rinses and gently mixed. Samples were taken at 0, 1, and 5 minutes. Samples were neutralized by adding aliquots from the assays to Neutralizing Broth® (Difco). Aliquots from these tubes were spiral-plated and incubated either in 5% CO2 or anaerobically in a Coy chamber. Numbers of viable bacteria were determined by standard spiral-plating methodology. Data were analyzed via a one way ANOVA. Results: ClosysII exhibited strong bactericidal activity with killing of most test organisms within a matter of minutes. The activity observed was equivalent to all rinses tested with no significant differences observed between the rinses. Conclusion: The CloSYSII stabilized chlorine dioxide rinse exhibited significant bactericidal activity against the bacterial species tested and performed at an equivalent level to the other rinses. Supported by Rowpar Pharmaceuticals Co., Inc.