The mismatched CYP2C9*3 DNA was detected by a exciplex fluorescent-probe system. The exciplex fluorescent-probe model system comprises of two 12-mer oligonucleotides fluorescent-probes, complementary to neighbouring sites of a 24(47) -mer DNA target and plasmid target, each equipped with moieties able to form an exciplex on correct, contiguous hybridization. Very similar results were obtained between the 24-mer target and the 47-mer target when WT and MT systems were detected by the exciplex fluorescent-probe. Exciplex bands at 505 nm were found for both 24(47)-mer WT and 24(47)-mer MT-targets at 5 ℃ , but were not distinctive enough to distinguish 24(47)-mer WT-target and 24(47)-mer MT-target. However the experiments were carried out at Tm, the exciplex band disappeared almost completely for 24(47)-mer MT-target system like control system, and there was still a strong exciplex band for the 24(47)-mer WT target system. Exciplex peaks at 505 nm were seen for the WT circular plasmids system, but not for MT circular plasmids. Therefore, mismatches of CYP2C9*3 DNA can be effectively detected by this exciplex construct, giving potential for single nucleotide polymorphism detection.