Deuterium oxide (D₂O, heavy water) is a moderator in nuclear reactors and has the cytotoxic effects oil various cancer cells, depending on their origin. We Studied the cytotoxic effects of the morphological changes and proliferation patterns for the urological cancer cells lines, the renal cancer cell lines A-498, the prostate cancer cell lines DU-145, and the bladder cancer cell lines T-24, mediated with 25 and 50% D₂O mixtures in pure water. These were studied with different concentrations of D₂O in the search for a new modality of treatment. T-24 showed a marked reduction in cells at both low and high concentrations of D₂O. DU-145 showed mild proliferation in the beginning and became cytostatic in the later stages at low concentrations of D₂O, but at a high concentration, the number of cells DU-145 was constantly reduced. A-498 showed constant reduction at both low and high concentration less than T-24. Morphologically, some of the cells showed condensation of chromatic material around the periphery of the nucleus and increased vacuolization of the cytoplasm suggesting apoptosis. And, other cells showed haziness and irregularity of the Outline of the cell which interruption indicates necrosis. We concluded that there is the cytotoxicity mediated with the concentrations of D₂O in urological cancer in which induces by both apoptosis and necrosis.