Various solution-treatments were applied on a rapidly solidified and subsequently rolled Mg-7.50Al-1.07Ca-0.17Mn (mass%) alloy sheet, and a room-temperature stretch formability, tensile properties, microstructures, and textures of the solution-treated sheets have been investigated. Although the solution-treatment at 400 °C gives high strengths, the sheet shows poor room-temperature stretch formability with the Index Erichsen value of 4.8 mm due to densely dispersed second phase particles. Also, the particles tend to distribute to the rolling direction, leading to limited elongation to failure of 11.0% along the transverse direction. The solution-treatment at higher temperature leads to the sparse and relatively uniform dispersion of the particles. This results in the significant improvement in the room-temperature stretch formability and ductility. The Index Erichsen increases to 6.8 mm by the solution-treatment at 450 °C for 4 h, and the sheet shows large elongation to failure of 19.1% and 17.1% along the rolling and transverse directions, respectively. The sheet also exhibits high strengths and in-plane isotropic properties, tensile strength over 320 MPa and 0.2% proof stress of ~180 MPa could be obtained due to fine grain structure with the average grain size of 9.5 μm.