A method for preparing a novel recombinant DNA, which comprises (1) cleaving with an endonuclease a phage DNA having an endonuclease-sensitive region not in the DNA segment participating in temperate phage DNA replication and integration of DNA into a host chromosome but in other DNA segments, a temperate phage DNA having an endonuclease-sensitive region in the DNA segment carrying genetic information for the production of coat protein, and a DNA carrying the intended genetic information, (2) mixing together all fragments produced by said cleaving, (3) adding DNA ligase to the mixture, and (4) recovering from the resulting mixture a phage DNA having its coat protein producing ability deleted by the replacement of the DNA segment carrying genetic information for coat protein production with a DNA fragment carrying the intended genetic information.