The superplastic behavior of Al-5%Mg-1.2%Cr alloy prepared by rapid solidification technique was investigated in the temperature range of 645 to 828K. The maximum ductility exhibited by the alloy was approximately 1100%, which is larger than that of other superplastic aluminum alloys. Also, the optimum superplastic properties were achieved at much higher strain rates than other aluminum alloys. This result is attributed to the presence of fine precipitates which maintain a fine grain size in the Al-Mg-Cr alloy at high homologous temperatures. The alloy behaves as a class II solid solution (stress exponent, n, equals approximately 4.5) in the lower strain rate range of 6.7×10＾(-5) to 3.3×10＾(-4) S＾(-1). Substructural observation revealed the tendency for subgrain formation in this strain rate range. At higher strain rate of 3.3×10＾(-2) to 6.7×10＾(-1)S＾(-1) and above 699K superplastic deformation was observed. Substructural observation showed some evidence of heavy dislocation activity without a tendency for cell formation. Above the strain rate range of superplastic behavior the alloy behaves as a class 1 solid solution (n=3) and power law breakdown occurs above about ε˚/ D = 10＾(14)㎡.