The nickel-based superalloy GH4099 was diffusion-bonded with 2-10m thick pure nickel interlayer. The joint microstructure was characterized by scanning electron microscopy, electron probe micro-analyzer and electron backscattered diffraction; the joint mechanical properties were evaluated by nanoindentation, tensile and Charpy impact tests. It was observed that with the reduction in interlayer thickness, element distribution and hardness across the joining interface became more homogeneous and subsequently produced sound joints due to the suppression of precipitated carbides on joining interface. The strengths of joints were in the range of the base metal as-received. When bonding time or temperatures increased, the bond line of the 2m interlayer joint was partially eliminated by the recrystallization across the joining interface, and the strength and elongation (or the absorbed energy) of the joint were same as (or close to) the base metal which underwent the same heating process. However, due to the microstructure degradation induced by the grain coarsening, the absorbed energy of the 2m interlayer joint reaches the maximum when the joint bonded under the moderate condition of 1120 degrees C and 90min.