V₅₅Ti₃₀Ni₁₅ alloy seems to be a promising alloy as a potential replacement for Pd－based alloy, which may reach a good combination of hydrogen permeability and mechanical stability in hydrogen. Metal rolling process is most widely used for sheet fabrication and may make multiphase V－Ti－Ni metallic membranes being thinner for increasing hydrogen transport flux. Different heat treatment processes have been carried out on a selected V₅₅Ti₃₀Ni₁₅ alloy to soften for improved workability in this work. The effect of heat treated process on microstructure and hardness have been investigated for V₅₅Ti₃₀Ni₁₅ alloy by using hardness measurement, OM, XRD, SEM, EDS and TEM. The microstructures resulting from different heat treatment temperatures and time have a great influence on hardness. Fine NiTi particles precipitate from the V－based supersaturate solid solution when the alloys were heat treated at 750 and 800℃, and the amount of NiTi particles increases with time. Fine NiTi particles precipitate from the V－based supersaturate solid solution results in the decrease in hardness. With increasing temperatures, fine NiTi particles re－dissolve into V－based solid solution, and the alloys hardness increase instead. Solid solution hardening of Ni and Ti elements is greater than precipitation strengthening of fine NiTi particles formed by atomic binding of Ni and Ti in V₅₅Ti₃₀Ni₁₅ alloy. When the alloys were heat treated at 900℃, casting stress and lattice distortion decrease at heat treatment earlier stage, and then NiTi₂ phases start to aggregate and spheroidize on phase boundaries with extended time. This causes the phenomenon that the hardness first decrease and then increase.