This paper is concerned with a manufacturing process and technology to facilitate the economical manufacture of high-quality magnesium alloy sheets. Magnesium alloys AZ31, AZ61, AM60 and AZ91 were used to investigate the appropriate anufacturing conditions for use in twin-roll strip casting. Temperatures of the molten materials and roll speeds were varied to find the appropriate manufacturing conditions. The effects of manufacturing conditions on possible forming were clarified in terms of roll speeds and roll gaps between upper and lower rolls. In addition, microscopic observation of the microstructure of the finished casting was performed. It was clarified that a magnesium sheet of 2.5 to 4.5mm thickness could be produced at a speed of 20 m/min by a horizontal copper roll caster. It was also found that the cast magnesium sheet of AZ31, AZ61, AM60 and AZ91 manufactured by roll strip casting could be used for plastic forming if the appropriate magnesium sheets were produced after the roll casting process. By a warm deep drawing test, it also demonstrated that a limiting drawing ratio of 2.4 was possible in the case of AZ91 sheet that was difficult to be manufactured by conventional extrusion process or DC casting and hot-rolling process for magesium alloy sheets with high aluminium contents.