Grass carp(Ctenopharyngodon idellus)genomic fosmid library cotaining 129014 clones was constructed and characterized from one diploid grass carp.The average insert size of the fosmid library was determined to be 35 kb by pulsed field gel electrophoresis,which is 4.1-fold coverage of the grass carp genome.To demonstrate the probability of picking the functional genes from the library,eleven functional genes were screened by three-dimensional PCR technique.The number of positive clones of these genes was from 1 to 6.So,this library may screen any useful genes from grass carp.This grass carp genome fosmid library will be integrated in the presently ongoing efforts to determine the sequence of the grass carp genome.