This paper presents a route of an applied research and development, which is possible to be done for rejuvenation of superalloy components in the gas turbine industry. The re-heat treated microstructures of cast polycrystalline nickel base superalloy IN-738 turbine blades, operated by Electricity Generating Authority of Thailand (EGAT) for long-term services (70,000 hrs.), were investigated by optical microscope and SEM. It was found that microstructure of the exposed specimen after long-term service can be nearly recovered by a re-solution treatment followed by two-step aging treatments. During solution treatment, the coarse carbides and gamma prime precipitates were partially dissolved into the matrix. Then specimens were treated through series of aging resulting in uniformly dispersed precipitation of gamma prime particles, which is more uniform than those in the long-term exposed microstructure. However, it was also found that the higher solution annealing temperature resulted in less volume fraction of gamma prime precipitates and less homogeneous in microstructure than the lower one.