Diffusion bonding between W and steel using V/Ni composite interlayer was carried out in vacuum at 1050°C and 10MPa for 1h. The microstructural examination and mechanical property evaluation of the joints show that the bonding of W to steel was successful. No intermetallic compound was observed at the steel/Ni and V/W interfaces for the joints bonded. The electron probe microanalysis and X-ray diffraction analysis revealed that Ni 3 V, Ni 2 V, Ni 2 V 3 and NiV 3 were formed at the Ni/V interface. The tensile strength of about 362MPa was obtained for as-bonded W/steel joint and the failure occurred at W near the V/W interface. The nano-indentation test across the joining interfaces demonstrated the effect of solid solution strengthening and intermetallic compound formation in the diffusion zone.