The effect of a mixed powder on the wide gap transient liquid phase diffusion bonding of a directionally solidified Ni base superalloy, GTD-111 was investigated. The mixed powder consisted of a mixture of a powdered Ni base filler (GNi-3) and powdered base metal (GTD-111). The range of the base metal powder was 40 to 70wt%. Bonding was performed at a temperature of 1463K, using various holding time. In the case of a lower 50wt%, the base metal powders completely melted and base metal mating at the interface dissolved at an early time, and extent of dissolution of base metal decreased with increasing mixing ratio. Liquid was eliminated by isothermal solidification, which was controlled by the diffusion of B into the base metal. The solids in the bonded interlayer grew epitaxially from the mating base metal inward from the insert metal and the number of grain boundaries formed at the bonded interlayer corresponded with those of the base metal. The finishing time for isothermal solidification was about 74ks. In the case 60wt% and higher, the base metal powders partially melted and remained in the vicinity of bonded interlayer. The solid was formed from the remaining powder and base metal mating at the interface. Finally, the bonded interlayer underwent the poly-crystallization when isothermal solidification was complete. The contents of Al and Ti in the bonded interlayer with a holding of 74ks were equal to that of the base metal.