Abstract:This paper presents the method for synthesis in vitro of cDNA coding for alfalfa (Medicago sativa L. Vernol) leghemoglobin in detail. The first stranded cDNA was synthesized by using leghemoglobin mRNA as template with AM virus reve- rse transcriptase. Then the double stranded cDNA(ds-cDNA) was obtained from the first one with E. coli DNA polymerase Ⅰ. In order to construct the recombinant DNA, the two methods--addition of homopolymer tails and chemically synthesized restriction site Sal Ⅰ linker to ds-cDNA were adopted to join and ligate the ds-cDNA and plasmid pBR322 DNA together. The recombinant DNA was transformed to E. coli c600 and 75 transformants were selected according to anapecilin resistant and tetracycline sensitive colonies. Hybridization-selection and cellfree translation preliminarily demonstrated that the cDNAs from two colonies screened are homologous to the mRNAs of alfalfa leghemoglobins, but the characterization of the cDNAs, such as which components they are coded for should be futher investigated.