Spectral karyotyping (SKY) is a novel cytogenetic technique, has been developed to unambiguously display and identify all 24 human chromosomes at one time without a priori knowledge of any abnormalities involved. SKY discerns the aberrations that can not be detected very well by conventional banding technique and fluorescent in situ hybridization (FISH). So SKY is hyper-accurate, hypersensitive, and hyper-intuitional. In this paper the basic principle of SKY technique and its application in leukemia cytogenetics were reviewed.