Microstructures and room-temperature mechanical properties of GH4099 alloy fabricated by laser additive manufacturing after heat treatments are investigated. The results indicate that the microstructure of as-deposited sample is mainly composed of epitaxial growth columnar grains. After solution treatment at 1120 ℃, due to the occurrence of recrystallization, the columnar dendrites are replaced by fine equiaxed grains, and there are some twin boundaries in the grains. There is less difference in microstructures between the solution treated samples and the solution-aging treated samples, their microstructures are still composed of fine equiaxed grains, and the size of grains does not grow up. However, the γ′ phase precipitates in the γ matrix after the aging treatment. Compared with the tensile properties at room temperature of samples in three sates, it can be found that the solution samples have the lowest strength and highest plasticity, while the aging samples have the best performance with high strength and ductility at room temperature. The reason is that recrystallization fully takes place during the solution processing and the dislocation density is small, while the γ′ phase only precipitates after aging treatment, which can block dislocations movement.