In order to investigate the effects of chromium on the fracture characteristics of Al-2.5% Mg alloy, impact test was performed by means of instrumented charpy impact testing machine at low temperatures. And also their fractographies were observed by scanning electron microscope. From this study following results were obtained. 1) Impact values and fracture loads were markedly increased by adding chromium at -196℃, whereas the deflection was sharply reduced. 2) Each of these alloys showed Ei＜Ep at room temperature while Ei＞Ep at -196℃, but not regular at -78℃. 3) From the observation of fracture surface by scanning electron microscope, low temperature embrittlement as in iron and steel was not recognized. However, the toughness of Al-2.5 Mg alloy was increased by adding chromium at -196℃.