The horseshoe crab (Tachypleus tridentatus) is known as a living fossil. It plays a very important role in evolution and medical resarch. The horseshoe crab onced istributed widely along the west coast of Taiwan island decades ago. It was almost eliminated from the coast as a result of environmental pollution and degradation. Currently, Tachypleus tridentatus can only be found in Kimmen and Penghu islands. Tachypleus tridentatus in both islands arre still facing threat to its survival. The objectives of this study were to induce wild horseshoe crabs natural spawning under a designed system. Spawning occurred from June 6 to September 10 2007, and spawning peak period was July (53%). Water temperature ranged between 26.2 and 31.2 ℃.There were 74,504 horseshoe crab’s eggs collected. Eggs were then moved to the circulating water system for hatching- out. There were 18,460 1st instar larva and 624 larva molted into 2nd instar stage. Only 43 individuals were successfully molted into 3rd instar larva. After 231 days of hatching-out, it still had two that successfully molted into 4th instar larva.