The G-banding technique was performed on chromosomes from gill tissue of three cupped oyster species : Crassostrea gigas, Crassostrea angulata and Crassostrea virginica. Identification of the ten individual chromosome pairs was obtained. Comparative analysis of G-banded karyotypes of the three species showed that their banding patterns generally resembled each other, with chromosome pair 3 being similar in all three species. However, differences from one species to another were also observed. The G-banding pattern highlighted greater similarities between C. gigas and C. angulata than between these two species and C. virginica, thus providing an additional argument for genetic divergence between, these two evolutionary lineages. C. gigas and C. angulata showed a different G-banding patterns on the two arms of chromosome pair 7, which agrees with teir taxonomic separation. The application of this banding technique offers a new approach to specific problems in oyster taxonomy and genetics.