A reagent and method for detecting SNPs of DNA nucleotide sequences by using a single kind of beads of the same grain size are provided. Beads on which a probe is immobilized that hybridizes with a DNA nucleotide sequence having no SNP is mixed with beads on which another probe is immobilized that hybridizes with a DNA nucleotide sequence having SNP to make a reagent. The reagent is added to a sample solution containing a fluorescence-labeled DNA nucleotide sequence under investigation and hybridized. The beads after the reaction are flown in a flow cytometer to obtain a fluorescence intensity histogram pattern, based on which SNP of the DNA nucleotide sequence under investigation is determined.
