Al-Mg alloy sheets with high Mg contents (3~10wt%Mg) were fabricated by twin roll strip casting. The optimum process conditions to get a good surface quality of Al-Mg strip have been suggested in this experiment. Controlling the cooling rate of cast roll was important to improve the surface quality of the strip and a compositional homogeneity through the thickness. The size of intermetallic particle like Al-Fe compound was reduced down to 1~2μm due to a high cooling rate of Al melt during strip casting. In addition, the dendrite structure was fine and the segregation of Al8Mg5 phase between grains was remarkably reduced. Therefore, the strips with a thickness of 3mm have good workability during additional hot/warm rolling processes. The hot/warm rolled Al-5wt%Mg sheets show high strength and elongation. When the rolled sheets were annealed at 300 oC for 1hr., the tensile strength and total elongation of the sheets reached at 290 MPa and 30%, respectively.