To clone the phage SP6 RNA polymerase gene the Hind III digestion fragment containing the gene was first mapped with restriction endonucleases Bst XI, Dra I and Kpn I. The Kpn I cleaves the structural gene into two parts. The downstream three fifths of the gene from Kpn I site to Bst XI site was successfully cloned into the plasmid pUC19 and partially sequenced. Using the unique and common Hpa I site of the SP6 and T7 RNA polymerase genes, has been constructed a hybrid T7/SP6 RNA polymerase gene that contains the upstream two thirds of T7 gene and the downstream one third of SP6 gene, from the cloned SP6 and T7 RNA polymerase genes.