In the artificial hybridization between female grass carp(Ctenopharyngodon idellus)and male common carp(Cyprinus carpio), no hybrid embryos survived to hatching except a few gynogenetic grass carp and androgenetic common carp.Comparisons of karyotype and embryonic development between the hybrid and its parents(grass carp and common carp)showed that the chromosome number of hybrid embryos varied considerably, usually ranging from 24 to 73. Most chromosomes of common carp were gradually lost and aneuploid appeared in almost all the hybrid embryonic cells. A few embryos developed by means of gynogenesis or androgenesis. The difference in the rate of embryonic development between grass carp and common carp was distinct, and the characters of hybrid embryonic development were much closer to those of grass carp. Asynchronus development between plasma and male nucleus may be the cause for the continuous loss of chromosomes in the hybrid cells.