The alloying behavior, the microstructure and the high-temperature tensile properties of the Nb-added Ni-3(Si,Ti) alloys were investigated. The solubility limit of Nb element in the L1(2) Ni-3(Si,Ti) phase at 1273 K was shown to be approximately 2.7 at%, and thermodynamically discussed. The second-phases (dispersions) formed beyond the solubility limits were identified as D0(a)-type Ni3Nb and Ni(1)2Si(4)TiNb(2) compounds, and contained some lattice defects with incoherency with the L1(2) Ni-3(Si,Ti) matrix. The Nb-containing second-phase dispersions in the L1(2) Ni-3(Si,Ti) phase matrix resulted in strengthening over a wide range of temperature, and also an improvement of the high-temperature tensile elongation.