Abstract: The metaphase chromosome was prepared from velum larvae of oyster Crassostrea nippona. The karyotype analysis showed that chromosome number was 2n = 20 and karyotype formula 2n = 20m, NF = 40. There was no telocentric, subtelocentric and submetacentric chromosomes and polymorphism of the karyotype was not found, similar to most species in genus Crassostrea.