Abstract: Objective To determine whether there were any repetitive DNA sequences in the genome of Schistosoma japonicum.Methods Two sets of oligo-nucleotide primers were designed based on the repetitive DNA sequence unit in the genome of Schlstosoma mansoni and Schistosoma haematobium,respectively.Then,PCR amplifications were conducted with the genomic DNA of S.japonicum being the template.The PCR amplification was optimized using twelve PCR reaction buffers prepared in our laboratory,which proved to be highly efficient.Results Based on PCR optimization assays,repetitive DNA sequences similar to either one of these two repetitive DNA sequence units were successfully amplified(Sm1-7,specific to S.mansoni and the Dral repeat,specific to S.haemarobium).However,both repeats were much less presented in the genome of S.japonicum according to PCR assays.It was also noted that the S.mansoni-specific repetitive DNA sequence unit(Sm1-7)was better represented in the genome of S.japonicum than the S.haematobium-specific repetitive DNA sequence unit(the Dral repeat).Conclusion There might be a family of 121bp,repetitively represented DNA sequences in the genome of S.J aponicum.Further determination necessitated DNA sequence analysis.