Abstract. The effects of temperature and pH value on hydrolytic stability of Reactive Black 5, and the effects of pH buffer on pH value stability of dye solution and ink prepared by Reactive Black 5 are studied in this paper. The results show that the final pH value decrease with the increase of temperature, both elimination reaction rate and hydrolysis reaction rate of Reactive Black 5 increase with the increase of temperature, and elimination reaction is the main factor of affecting pH value of dye solution at low temperature, but hydrolysis reaction will become the main factor at high temperature. The increase of initial pH value can increase the decrease rate of pH value of dye solution in the beginning time, Reactive Black 5 can keep at equilibrium state of elimination reaction and hydrolysis reaction at the pH value of 4.4 and temperature of 40 °C, and the elimination reaction rate will increase with the increase of initial pH value at 40 °C. Adding pH buffers into dye solutions can significantly reduce the decrease extent of pH values, and the pH buffer of NaH2PO4/ Na2HPO4 has the strongest ability of stabilizing pH value, the increase of amount of NaH2PO4/ Na2HPO4 can reduces the decrease extent of pH value, and the initial pH value of dye solution increases with the increase of proportion of Na2HPO4 in the pH buffer. When applied in ink, NaH2PO4/ Na2HPO4 still has the strongest ability of stabilizing pH value while it has little effects on properties of ink.