A DNA array for detecting a single nucleotide polymorphism of a gene, which comprises, on a solid support, a first probe spots group consisting of one or more probe spots each containing one or more probes hybridizable with a polynucleotide of the gene, in which the probes are exactly complementary to the first polymorphism pattern of the gene, and a second probe spots group consisting of one or more probe spots each containing one or more probes hybridizable with the polynucleotide of the gene, in which the probes are exactly complementary to the second polymorphism pattern of the gene, wherein probe lengths in the probe spots is different from each other. This DNA array enables more exact SNP detection.