Objectives: Recently, a new electrolyzed water; PerfectPerio™ water (PPW; Noguchi Dental Medical Research Institute, Tochigi, Japan,) was introduced containing high concentrations of free chlorine (Okada A el at.,86th IADR) to control oral infections. However, the effects of PPW on the oral tissue have not been evaluated yet. Thus, the aim of this study is to investigate cytotoxic effects of PPW on human epithelial cell line (HeLa-KB). Methods: An MTT assay was employed to evaluate the effects of the PPW on KB cell proliferation and a permeability test was performed using fluorescence microscopy after staining with a LIVE/DEAD BacLightTM Bacterial Viability Kit. The KB cells were grown (1x104 cells/well) and incubated for 1-9 days. On the 3rd day of culture, 10sec treatment was performed with different functional chlorine concentrations of PPW; PPW1 (600ppm), PPW2 (300ppm), PPW4 (150ppm) and PPW6 (100ppm). Mineral water (MW), Listerine and 0.12%NaOCl were used as controls. MTT data were taken on day 1, 3, 5, 7 and 9 after treatment using 20µl of MTT solution in each well, followed by further incubation for 4 hours. Results: Statistically significant increase in Optical Density (OD) was observed in KB cells treated with PPW4 and PPW6. However, OD remained unchanged in PPW1 and PPW2 groups. Permeability tests displayed absolute co-relationship with MTT data as most of the cells fluoresced green indicating integrity in the nuclear membrane in case of PPW4 and PPW6 which was almost same as untreated and MW treated control groups on the 5th day after treatment. Conclusion: The results indicate that the 4 or 6 times dilution of original PPW concentrations can be considered for prophylactic treatment to control cariogenic and periodontal infections and would serve as very useful baseline information for further clinical studies. This study was supported by G-COE Program, IRCMSTBD at TMDU and Noguchi-DMRI.