The composition of a brazing-filler metal in an Ag-Cu-V system which was selected using lattice misfit data, was estimated using perturbation interface model and applied it to the brazing artificial single crystal diamond (111) by unidirectional-solidification brazing. An Ag-27.8Cu system containing less than 1mass%V brazing-filler metal provided stable joint strength (the shear strength at the brazed interface exceeded 200 MPa). Optical observation of the brazed interface revealed that silver crystal grains grew from vanadium carbide islands formed on the diamond. This behavior is consistent with a slight degree of lattice mismatch between silver and vanadium carbide crystals. Atomic force microscope observation revealed small scale islands of the reaction products with good adhesion are enough for brazing diamond (111). X-ray diffraction results indicated several types of vanadium carbides, V8C7, V4C3 and V2C were formed there, and V4C3 reaction product was considered to provide good adhesion between the filler metal and the diamond due to prefer solidification of silver on the reaction products islands.