Rice (Oryza sativa, L. n=12) is one of the most important crops in the world. Genetic and cytological studies on rice have been extensively carried out for more than 100 years. Since the rice chromosomes are rather small and similar in shape, it is not easy to identify each chromosome. Karyotype analysis of rice was almost impossible before the advent of successful chromosome preparation techniques. A fine correspondence between rice linkage groups and their chromosomes was not figured out until the chromosomes were appropriately defined in 1990. In the last ten years, fluorescence in situ hybridization (FISH) technique has been widely used in various areas of plant, including rice. It is still difficult to achieve reliable signals of single-copy genes. Recently success in mapping single gene on rice chromosome by FISH technique using BAC clones would be a new approach to physical map on rice chromosomes.