The microstructures of Mg-10Gd-3Y-1.2Zn-0.5Zr alloys after solution heat treatment at different temperatures comparing with the as-cast conditions were studied by using the optical microscope, XRD, SEM and TEM. The results showed that the LPSO lamellar phase grew with time increasing under the conditions of isothermal solution. At same time, the lamellar phase extending into grain which induced the lamellar to become widen. The original cast lamellar phase dissolution with the temperature increasing, however, a wider lamellar phase produced along compound located at the grain boundary. The new lamellar phase width increased with time. The alloy after solution treatment at 525℃ the sample hardness could reach 115 HV.