The goal of this work was to evaluate the safety and efficacy of the Red Light Emitted Toothbrush (R-LETB) emitting at wavelength of 663 nm with power density of 3.3mW/cm² in combination with 0.1%-methylene blue (MB) solution for the reduction of plaque and treatment of gingivitis. A microbiological in vitro study and a pilot clinical study were conducted. The microbiological study has shown total suppression of pathogenic flora after a 3-min exposure to the dye solution followed by a 20-sec treatment with the R-LETB. For the clinical study, 37 subjects of both sexes with gingivitis were enrolled and randomly assigned to one of two groups. Subjects in the first (treatment) group were instructed to rinse their mouth with MB solution provided for 1 min and then brush the teeth with the R-LETB and standardized toothpaste. The second (control) group used only the toothpaste and a regular toothbrush. Subjects in both groups followed their respective procedures 2 times a day (morning and evening) for 30 days. Indices of plaque, gingival bleeding, and inflammation were evaluated at 14-day and 30-day timepoints. In the both groups, all indices improved in comparison with baseline. However, the treatment group demonstrated more pronounced improvement of the studied indices that was attributed to additional anti-microbial action of red light and MB on gum tissue. Thus, the use of R-LETB with MB appears to have a multifactor therapeutic action on oral pathological microflora: mechanical removal of the bacteria and suppressing action on microorganisms due to photodynamic reaction.