Nb-Si superalloy is one of the most potential structure-materials of next generation aero engine. The influence of rare-earth element Gd on microstructure and mechanical properties of Nb-16Si-24Ti is explored in this paper. Results show that phase composition no change by doping of Gd. And the mass of Nbss/(Nb, X)3Si eutectic exists in the matrix instead of primary Nbss. The rare-earth element Gd reduces the Si contents in Nbss phases, and the content of O is also limited because of its high active. The deflection, bridging and secondary crack are easily found in coarsened Nbss, and the peak-value of fracture toughness is 8.37 MPa·m1/2 in NST-0.05Gd alloy. The phenomenon of solution strength is obvious, and the maximum value of RT compressive strength is 2214 MPa. The thermal compression test indicates that silicide phases play the major role for high-temperature performance, and the Nbss phases have the poor heat-resistance under HT condition.