Growth and spawning of Crassostrea rivularis inhabited in estuary of Gahwacheon, Sacheon, Gyeongsangnam-do, Korea were investigated from June 1995 to August 1996. The shell height of two-year oyster ranged from 56.7 ± 4.8 mm in October to 87.7 ± 24.6 mm in June, and that of three-year oyster was from 123.0 ± 24.7 mm to 133.2 ± 10.5 mm. Condition factor was in a range from 0.0409 ± 0.0138 (October) to 0.0732 ± 0.0267 (July), and it began to increase in December. It reached the maximum in July, then decreased rapidly thereafter. The spawning period was determined to be July and August on the basis of monthly changes in condition factor and relative growth of meat weight to shell weight.