Comosomal polymorphism involving constitutive heterochromatin has been reported in mu, pigs, mouse, horse, chicken and so on. The chromosomal polymorphism of Japanese quail which includes constitutive heterochromatin as well the chromosomes without banding treatment has now been found. Through the use of a general technique that permits visualization of chromosome morphology and heterochromatin, three chromosomal variants have been found among birds ； ＋/＋ homozygous from, ＋/－ heterozygous form and －/－ homozygous form in chromosome 4. This variants appear to be common in the randombred population and stably inherited in a Mendelian fashion. These results suggest that the variants would be useful as chromosomal markers for various types of cytogenetic studies.