Hydroxyapatite (HA) has been evaluated for use in a variety of applications in bone reconstruction surgery because of its high affinity with host bone and biocompatibility. However, because of the difficulty in combining porosity (for bone ingrowth) and strength in HA, it is generally considered inappropriate to use HA for high-load applications such as spinal interbody fusion. In the present study, we constructed a HA implant for spinal interbody fusion, composed of a dual HA composite (DHC) that combines two HA materials with different porosities: HA with 75% porosity, for bone ingrowth; and HA with 0% porosity, for load bearing. We used a canine lumbar interbody fusion model to evaluate bone conduction of the implant and its efficacy for bony fusion. Six months after the operation, DHC exhibited almost the same efficacy for bony fusion as iliac bone grafts. Moreover, pores of the porous part of the DHC were completely filled with newly formed bone and bone marrow cells. The present findings indicate that DHC is suitable for use as an implant material for spinal interbody fusion as a substitute for iliac bone grafts, which could eliminate the disadvantages associated with autograft harvesting.