The rates of hydrolysis of sodium pyrophosphate and triphosphate in solution have been measured at 65.5 °C. over the pH range 2.0 to 12.0 and the phosphorus concentration range 0.10 to 0.25 atomic weights per liter. The reactions were found to be first order providing a constant concentration of hydrogen ion was maintained in the reaction flask. Both reactions are acid catalyzed but only the hydrolysis of triphosphate was found to be base catalyzed. Pyrophosphate and triphosphate apparently hydrolyze independently of each other.