A DNA synthesis method with a shortened time period required for DNA synthesis by polymerase chain reaction (PCR), characterized in that a DNA polymerase is used in an amount effective for providing more than 10 ng of amplified DNA fragments of about 2 kb per 50 mul of a reaction mixture, when PCR is carried out under the following conditions (A) and (B): (A) reaction mixture: 50 mul volume of a reaction mixture comprising DNA polymerase, 1 ng of genomic DNA from Escherichia coli, and 10 pmol each of primers Eco-1 and Eco-2 (nucleotide sequences of the primers Eco-1 and Eco-2 being shown in SEQ ID NOs: 10 and 11 of Sequence Listing, respectively); and having a composition suitable for the DNA polymerase; and (B) reaction conditions: 35 cycles of PCR, wherein one cycle consists of 99° C., 1 second-66° C., 7 seconds; a kit for DNA synthesis usable for the DNA synthesis method; and an article of manufacture of a PCR agent. According to the present invention, the procedures in the genetic engineering studies and industries involved with PCR can be speeded up.