The rapid dendritic growth of primary Ni₃Sn phase in undercooled Ni-30.9%Sn-5%Ge alloy is investigated by using the glass fluxing technique. The dendritic growth velocity of Ni₃Sn compound is measured as a function of undercooling, and a velocity of 2.47 m/s is achieved at the maximum undercooling of 251 K (0.17T_L). The addition of the Ge element reduces its growth velocity as compared with the binary Ni₇₅Sn₂₅ alloy. During rapid solidification, the Ni₃Sn compound behaves like a normal solid solution and it displays a morphological transition of “coarse dendrite–equiaxed grain–vermicular structure" with the increase of undercooling. Significant solute trapping of Ge atoms occurs in the whole undercooling range.