Reproductive ecology of the sharp toothed eel, Muraenesox cinereus was investigated based on the samples captured in southern Korean waters from January 2010 to December 2011. Gonadosomatic index began to increase in April, and reached maximum between July to August. After spawning it began to decrease from October. Reproductive season was estimated to April-September, with peak in July. Fecundity was proportional to the size of the female, with the clutch size varying from 56,000 eggs in the smallest female (anal length, 27.0cm) to 1,400,000 eggs in the largest (anal length, 49.5cm). Size at 50% sexual maturity ($AL_{50}$), determined from mature females, were 21.9cm. Annual reproductive cycles of this species could be divided into four successive stages; immature stage (October-February), maturing stage (March-May), mature stage (June-August) and spent stage (August-October).