A species of enigmatic amoeba was found front the oysters culcured in Jinhae Bay and the Goje Bay in September-October 1978 and October 1979. Occurrence and the morphological characteristics of the amoeba were studied. Based on their peculiar morphological characters the enigmatic body was a species of parasitic amoeba. The amoebas were morphologically very similar to the amoeboid parasite described by Sawyer(1977). Occurrence of the oysters infected with the amoeboid ranged from zero to $13.3\%$. The infection rate did not show any relations to the depth of water where the oysters were suspended. The longest diameter of the amoeba is $24;mu$. The thin outer membrane is lightly stained with eosin and PAS positively. Initially one amoeboid was found in an ovum, and later it propagated to 3 to 4 individuals.