This paper describes the twin roll casting technology of magnesium alloys that contains relatively high weight ratio of aluminum, such as AM60, AZ91 and AZ121. The cast magnesium alloy sheets were hot-rolled in an elevated temperature to investigate the appropriate hot-rolling conditions for producing high-quality strip using a purpose-built strip-casting mill. The influences of such process parameters as materials of roll, casting temperature, and roll speed are ascertained. A simple method of predicting the convection heat transfer coefficient between casting rolls and molten metal is introduced. The microstructure of the manufactured wrought alloy sheets was observed to investigate the effects of the hot-rolling and heat-treatment conditions on crystal growth in the cast products. It is found that manufacturing thin magnesium alloy sheet was possible at a roll speed of 110m/min by a vertical type roll caster. The grain size of the manufactured wrought magnesium alloys sheet was less than 30 micrometers due to rapid solidification in the proposed process.