The effects of increasing Al and decreasing Nb on microstructure and mechanical properties of GH706 alloy were studied. With increasing Al from 0.35% to 1.26% and decreasing Nb from 2.88% to 1.98%, the precipitation of γ″-Ni3Nb phase is constrained, while the formation of γ′-Ni3Al phase is promoted. As a result, the tensile strength at room temperature is decreased, but the impact energy is improved. However, such a modification of Al and Nb constrains the precipitation of intergranular η-Ni3(Ti,Nb) phase, and enhances the precipitation of Laves phase rich in Nb and Cr2Nb phase rich in Nb and Cr, which decreases the grain boundary cohesion and deteriorates the stress rupture properties at 650 oC and 690 MPa