Abstract Reproductive cycle of ascidiacea, Styela plicata were investigated by histological examination. The specimens were sampled in the coastal waters of Yeosu, between March 2008 and February 2009, was analyzed. Maturation cycle parameters such as the condition index (CI), oocyte size-frequency of gonad developmental stages in the gonads were analyzed monthly for the 30 samples. The condition index showed the highest value of 0.30 in April and the lowest value of 0.15 in August. The reproductive cycle can be grouped into the following successive stages: early growing (March to May), growing (June to August), mature (June to September), Spawning (March to July), and Resting & Recovery (October to April). This research will help improve the sustainable production of the resource and is important for future aquaculture development of this species that requires artificial harvesting techniques.