To provide a method for detecting a single nucleotide polymorphism of CYP2C9 (human cytochrome P450 2C9 gene) easily and useful for prediction of adverse effects by medicine metabolism in a patient.

This method for detecting the polymorphism of the human cytochrome P450 2C9 gene, presenting in a subject is provided by using at least one of an oligonucleotide consisting of a specific base sequence having continuous 18-28 bases or another oligonucleotide having specific base sequences of continuous 18-28 bases as a primer, and performing the examination of the gene polymorphism of the cytochrome P450 2C9.