In order to produce AZ91 and AZ31 magnesium alloy billets semisolid continuous casting by using an inclined cooling plate was carried out. The molten magnesium alloy in an electric furnace was flowed on the inclined cooling plate and then poured in a tundish. The slurry prepared using this process was solidified by drawing a dummy bar from a water-cooled copper mold, consequently producing a billet. As a result, we could produce the magnesium alloy billets by semisolid continuous casting. Magnesium alloy billets with refined and globular primary α crystals were successfully and continuously cast by optimizing the solidification conditions. In this case, the grain size of AZ91 billets was about 55μm and that of AZ31 billets was 50μm. The AZ91 billets produced by semisolid continuous casting were employed in thixocasting experiments. The experiments revealed that thixocasting could produce the mobile phone casings with spherical primary α crystals at 858K. Moreover, we proved that the difference of shot cycle did not influence the microstructures for up to 251 shots.