Abstract: Solution treatments of as cast GW83 magnesium alloy at different temperature and time were carried out.The effects of solution treatment on the microstructure and hardness of GW83 magnesium alloy were studied by OM, SEM, EDS and hardness test.The results show that the microstructure of as cast GW83 magnesium alloy is mainly composed of α-Mg, a large amount of continuous Mg₂₄ (Gd, Y)₅ phase and a small amount of granular Mg₅ (Gd, Y) phase. With the increase of solution treatment time, the grain size of GW83 magnesium alloy increases gradually, and the hardness increases first and then decreases.The Mg₂₄(Gd, Y)₅ phase at the grain boundary of GW83 magnesium alloy in solid solution at 525 ℃×4 h is mostly dissolved, the grain size does not grow significantly, and the hardness of the alloy reaches the maximum of 82.6 HV.525 ℃×4 h is the ideal solution treatment process for GW83 magnesium alloy.