Abstract: Combining cell synchronization in vitro and bromodeoxyuridine (BrdU) incorporation in early synthesis phases and late synthesis phase of cells of Ctenopharyngodon idellus,two kinds of chromosome patterns of replication banding,R- and G-bands were gained after chromosome preparation were irradiated in warm CaCI2 solution by UV and were stained with Giemsa.Some spreads lengthcncd in late-prophase and prometaphase show more numbers of bands and characteristics of higher resolution.Analysis of G-banded karyotype showe that there are four pairs of chromosomes with satellite.A tentative idiogrammatic representation of G-banded karyotype of Gtenopharyngodon idellusis proposed.The significance,techniques and possible meehanism of chromosome banding of fish are discussed.