Two kinds of martensitic phases (α-double prime phase with an orthorhombic structure and hexagonal ω phase) usually form in Ti-Nb-based shape memory alloys. In a Ti-30 wt.% Nb alloy with the addition of small amount of Pd, the size of the ω-particles becomes much fine in the as-cast state, and a novel martensitic plate-shaped ω phase was found for the first time in a water-quenched sample. It is suggested that the Pd addition can stabilize the b phase and suppress the coarsening of brittle ω-particles in as-cast state and modify the equiaxial grain with internal dendrites in the Ti-30Nb alloy to only the equiaxial grain in the Ti-30Nb-3Pd alloy, resulting in the ductility improvement. Various kinds of nanoscale twin structure of the α-double prime  martensitic phase will also be presented in the present work.Two kinds of martensitic phases (α-double prime phase with an orthorhombic structure and hexagonal ω phase) usually form in Ti-Nb-based shape memory alloys. In a Ti-30 wt.% Nb alloy with the addition of small amount of Pd, the size of the ω-particles becomes much fine in the as-cast state, and a novel martensitic plate-shaped ω phase was found for the first time in a water-quenched sample. It is suggested that the Pd addition can stabilize the b phase and suppress the coarsening of brittle ω-particles in as-cast state and modify the equiaxial grain with internal dendrites in the Ti-30Nb alloy to only the equiaxial grain in the Ti-30Nb-3Pd alloy, resulting in the ductility improvement. Various kinds of nanoscale twin structure of the α-double prime martensitic phase will also be presented in the present work.