The extruded Mg-12Gd-3Y-0.4Zr alloy sheets were rolled from 30 mm to 2.3 mm at 723 K by electric heated rollers, and then different heat treatments were performed to improve their properties. The microstructures and tensile properties of the alloy sheets were investigated, including as-rolled, annealed and T5 treated. The experimental results show that the grains are effectively refined by the rolling process, and the strength of the rolled alloy is greatly enhanced. The annealed alloy exhibits lower strength and higher elongation than the rolled one, while the aged alloy shows higher strength and lower elongation. After being aged at 498 K for 17 h, the alloys get the highest strength, namely, the ultimate tensile strength is 456.8 MPa, yield strength is 348.9 MPa, and elongation is 3.8%.