The object of the present invention is to provide a method of producing antisense oligonucleotide, in which the possibility of forming a substantially complementary double-stranded chain between each region of a nucleotide sequence in mRNA and a region other than said region is expressed as a numerical value, and oligonucleotide substantially complementary to a region with a smaller numerical value is prepared as antisense oligonucleotide. The resulting antisense oligonucleotide can be used effectively in the antisense oligonucleotide method.