The morphological relations and physiological characteristics of the triploid and diploid oysters (Crassostrea gigas) in Taean area, west coast of Korea, were investigated from May 2012 to April 2013. Mophometric analysis indicated that the triploid oysters have the same shell length to shell height ratio but higher shell depth to shell height ratio than diploids. Consistent with morphological characteristics, triploid oysters showed greater values of fatness, condition index and RNA/DNA ratio during the period of experiment. The DNA concentration in adductor muscle and mantle of triploid were either lower or equal to the nucleic acids of diploid. However, RNA/DNA ratio were significantly higher than diploid. It appears that RNA/DNA ratio could be a useful indicator of health condition of triploid and diploid oysters when taken in correlation with the morphological indices.