Using the mRNA prepared from hybridoma DW₁₀ secreted monoclonal antibody against human D-dimer as a template, the cDNA fragment encoding the V_k domain was amplified by reverse transcription and polymerase chain reaction (RT-PCR) with a set of universe primers that were on the FR1 region and FR4 region of V_k domain respectively.The RT-PCR product was ligated with pUC18. The result obtained from the restriction enzyme fragments and DNA sequencing showed that the length of the V_k was 330 bp, and the distinctive structures of the immunoglobin CDR1，CDR2 and CDR3 bf V_k gene appeared.