Aim: To determine the in vitro bactericidal activity of different chlorhexidine (CHX)-based commercial mouthwash products claiming different chlorhexidine concentrations under conditions similar to their use. Method: Bactericidal assays were performed using four major bacterial species implicated in periodontal disease: Fusobacterium nucleatum CIP101130, Aggregatibacter actinomycetemcomitans CIP 52.106T, Prevotella intermedia CIP 103607, and Porphyromonas gingivalis CIP 103683. Seven commercially available mouthwash products were chosen, each containing CHX digluconate (concentrations ranged from 0.1% to 0.2%) as the principle active ingredient. Assays were performed according to European guidelines for antiseptics (with modifications to mimic conditions of use) by exposing bacterial suspensions to the mouthwash solutions for 1 min ± 5 seconds at 32 ± 1°C in the presence of an interfering substance (artificial saliva). The log reduction in bacterial count was determined. Results: Five of the tested mouthwashes were defined as bactericidal to each of the four test strains (log reduction ≥ 5). However, two mouthwashes were not defined as bactericidal to all test strains (log reduction <5). In one case, a 0.12% CHX mouthwash was not bactericidal towards A. actinomycetemcomitans. In the other case, a 0.2% CHX mouthwash was not bactericidal towards two test strains, A. actinomycetemcomitans and P. intermedia. Conclusions: This study emphasizes that antimicrobial activity of CHX-based mouthwash products is not determined lonely by the CHX concentration, but by all the components of the formulation as a whole. Indeed, interactions between CHX and the different components, and not only alcohol, may affect antibacterial activity positively or negatively.