New ternary metal nanocrystals of Fe1-xPtMx (M = Ru3+, Sn2+, or Ni2+) were synthesized by chemical transformation from FePt nanocrystals using a cation redox reaction in a solution. The structure and composition of resulting nanocrystals were characterized by high-resolution transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and X-ray photoemission spectroscopy (XPS). Moreover, X-ray absorption near-edge spectroscopy (XANES) was employed to confirm the chemical transformation from FePt to Fe1-xPtRux nanocrystals. The analyses of extended X-ray absorption find structure (EXAFS) revealed the detailed binding structures and coordination numbers of both FePt and Fe1-xPtRux nanocrystals. The results suggested that iron atoms of FePt lattices were oxidized to be Fe2+ and Fe3+ ions and were replaced by ruthenium atoms from the reduction of Ru3+ ions in solution to form Fe1-xPtRux lattices. Our method has opened a new route to easily and rapidly prepare a solid-solution type of ternary metal nanocrystals for catalytic applications.