|In order to study the reproductive physiology of Sand eel(Hypoptichus dybowskii) catched at Kangwon-do, Wooamjin Bay, spawning and egg development were investigated in April and May, 1996. The obserbed spawning period was from the middle of April to the end of May with the water tempera-ture above 8캜. Body size and colouration were distinguished between male and female. The type of tes titular structure is lobular, and the ovary is a pair of sac-shaped covering with a fibromuscula capsule and comprising a mature egg of average 86. The unfertilized egg are demersal and adhesive, and their diam-eter were 1.65-1.95 mm. The colour of yolk is light yellow and contained a lot of tiny oil globules. The average spawned egg was 62 in sargasso weeds. Hatching was observed in 12 days after fertilization with the water temperature of 14*1봀. The average size of larva after hatching was 6.85+0.23 mm in total length, and larva were containing yolk including globule.