Abstract: The phase transformation temperature T_α+β→β from α + β phase to β phase of Zr-4 and N36 zircaloys was determined by metallographic method. The results show that the phase transformation temperature T_α+β→β of zircaloys could be determined by metallographic method. By quenching the samples at the temperatures near the phase transformation temperature T_α+β→β and then observing the change of α phase contents, the temperature range of incomplete transformation and complete transformation of α phase was determined, and the lower limit value of the temperature range was taken as the phase transformation temperature T_α+β→β. The recommended heat treatment heating temperature interval was 10℃. The measured T_α+β→β of Zr-4 zircaloy was 970℃, and the T_α+β→β of N36 zircaloy was 890℃.