The MUSES-C was launched on May 9th, 2003. It was renamed "Hayabusa" (falcon in Japanese). The spacecraft is a kind of technology demonstrator with five key technologies including the use of ion engines in interplanetary cruise as a primary propulsion means. After the flight of 2 years, Hayabusa arrived at the asteroid 1998SF36 (It was renamed "Itokawa") on Sep 12th, 2005. This paper presents the trajectory synthesis technique and results for Hayabusa. For this Hayabusa's trajectory synthesis using the electrical propulsion, it was important to allow enough time for the electrical propulsion operation for assuring the margin. And taking the multi-staged approach made it easier to cope with the problems that unexpectedly happened. Hayabusa's Trajectory Synthesis actually incorporated and demonstrated these points, and had coped with and had overcome all the difficulties, incidents such as the loss of reaction wheels (RW) and finally and successfully achieved the rendezvous with Itokawa.