In the case of using a blocking nucleic acid to prevent non-specific hybridization of a target nucleic acid with a nucleic acid probe, further excellent efficiency of detecting the target nucleic acid is achieved. A buffer composition used in hybridization of a target nucleic acid with a nucleic acid probe, wherein the buffer composition for hybridization contains a blocking nucleic acid comprising a nucleotide sequence complementary to a region comprising at least a non-detection target nucleotide in a non-target nucleic acid, in a concentration of one or more times higher than the concentration of a nucleic acid in a nucleic acid mixture consisting of the target nucleic acid and the non-target nucleic acid.