Abstract: The effects of reaction time, temperature, pH and amount of the components on the labeling efficiency of ~(99)Tc~m-N4AIPO are systematically investigated. The labeling efficiency is 95% under the optimum labeling conditions. The effective quantity of N4AIPO in kit is determined by HPLC. The stability of the kit under various stock conditions is also examined. The results show that the kit is stable, and the radiochemical purity is keeping more than 90%, or at 0~4 ℃ for 6 months, at room temperature for 2 months, or in 40 ℃ water bath for 10 days. In addition, the acute toxicity of the kit is low.