Kangen Water is water produced from water ionization machine by using an electrolysis process. The machine that is used to produce Kangen Water is able to restructure ordinary water and convert it into alkaline water. This research aims to determine whether or not Kangen Water has cytotoxic and anti-proliferative activity against T47D breast cancer cells. The Kangen Water that was used in this research was from one of the producers addressed in Sumampir, Purwokerto. The cytotoxic test in this research was performed by using MTT assay method with 24 hours incubation time, while cell proliferation was performed by using doubling time method. The cytotoxic test on Kangen Water showed a potential moderate cytotoxicity at pH 9 (IC50 46.611 %). The treated T47D cells were having a cell amount reduction during 24 to 72 hours. The sampling of Kangen Water by using pH 6 with 12.5% concentration could decrease the proliferation of cell T47D better than other pH in various concentrations.