Using methods based upon the PCR, two DNA sequences which are identical to two JH genes(accession No.AY158087 ， AY149283) from one Holstein bovine genomic DNA have been cloned, the results demonstrate that all the two JH genes(accession No.AY158087 ， AY149283) are present in the same Holstein bovine genomic DNA. Two kinds of IgM cDNA was cloned from bovine spleen total RNA. Sequencing the cDNA clones show that the last exon of JH gene (accession No.AY149283) JH6 is a functional gene encoding part of CDR3 and whole FR4 region of bovine IgM. The sequences of two IgM cDNA clones indicate each constant region is identical to one of the two Cμ genes(accession No.AY230207 ， U63637), there are greater diversities in the IgM CH1 domain than the other CH domains. PCR products of JH-Cμ gene suggested that each Cμ gene (accession No.AY230207 ， U63637) is in series with the same JH gene (accession No. AY149283) in the bovine germline genes, they are all functional genes in the process of bovine IgM generation.