An experimental approach has been used to ascertain the effectiveness of semi-solid roll strip casting of magnesium alloys using a twin roll caster. It has been recognized that semi-solid forming contributes to lightening the total product weight if semi-solid material produced by light metals can be used to replace conventional iron and steel products. However, the problems of utilizing magnesium alloys are still mainly related high manufacturing cost. This means that improved quality must be balanced by economic validity. In this experiment, magnesium alloy AZ31, AZ91, AM50 and AM60 were used to determine which were appropriate for use in semi-solid roll strip casting. Temperature of the molten materials, roll speeds at upper and lower rolls, which could be changed independently, were varied to find an appropriate manufacturing, condition. Effects of cooling and contact condition on possible forming were clarified in terms of contact condition between molten material and roll. Also, microscopic observation of the crystals of the finished casting has been performed. It has been found that magnesium sheet with 2.5 to 4.0 nun thickness could be produced at a speed of 30m/min.