The effects of temperature difference between egg yolk and water during cooking on the shell crack of hard cooked eggs were investigated. Water temperature was raised 0.5, 1, 2, 4 and 6℃ per minute respectively until yolk center temperature became 100℃. Crack rate increased more considerably as heating speed was rapider per unit time. There was a significant positive correlation between shell crack and temperature difference during cooking. Shell crack occurred more at maximum temperature difference(MTD) than at average temperature difference (ATD). The coefficient and regression equation with MTD and ATD were R=0.96, Y=0.9371X-2.8 and R=0.88, Y=1.843X-4.21, respectively.