The sequence of a defined DNA primer can be detected easily by a method described as below. A PCR (polymerase chain reaction) was carried out with the primer to be detected and one of the M13 universal sequencing primers. The resulting PCR fragment was purified and inserted into a pUC-18 or pUC-19 at the multicloning sites. Then the sequence of the primer to be detected can be exactly known by sequencing the recombinated plasmid with a M13 universal sequencing primer.