A blunt-end DNA cloning vector, pRSK116, was constructed. This vector was derived from pBR322 by opening with Sal I restriction endonuclease, filled with only TTP by Klenow fragment, trimmed with S1 unclease, and ligated with T4 DNA ligase. It appeared that the removal of three bases in the middle region of Tcr gene did not change the genetic property of the marker gene of the pBR322 and the unique Hinc II site in the Apr gene of the modified plasmid pRSK116 endowed improved property for the selection of recombinants. The Hinc II site has been tested for the cloning of blunt-ended human DNA. The recombinant colonies selected were Ap sensitive and Tc resistant and inserted DNAs were easily recovered by Hinc II treatment.