A cold crack criterion for JIS ADC12 aluminum alloy die casting is proposed. Through investigating the temperature dependence of the fracture strain of JIS ADC12 aluminum alloy die casting, it was found that the fracture strain features a turning point at a temperature, T_c (we called “critical temperature to the ductility”, about 573 K for the present composition), i.e. stays low while below T_c, rises rapidly to a high level beyond T_c. Focusing on this character of the fracture strain, we analyzed the equivalent plastic strain (ε_c) of the castings introduced below T_c in casting processes by thermal stress simulations and compared with the occurrence of cold cracks in the die casting experiments. It was found that the ε_c of the cracking positions in the castings exceeded, while the ε_c of the castings without crack were much lower than the fracture strain of JIS ADC12 aluminum alloy die casting below T_c. That is to say, the occurrence of the cold crack in a die casting can be judged by comparing the ε_c with the fracture strain below T_c. Based on this proposed criterion, it is possible to predict the appearance of the cold cracks in ADC12 die castings by thermal stress simulations.