Abstract: Success or failure of unmethylated cytosine conversion treatment is determined by using a first primer set comprising plural primers that hybridize with a nucleic acid comprising a nucleotide sequence not containing cytosine in the nucleotide sequence of biological DNA that is subject to an unmethylated cytosine conversion treatment and a second primer set comprising plural primers that hybridize with a nucleic acid comprising a nucleotide sequence in which cytosine in a nucleotide sequence containing cytosine and not containing a CpG site is converted into a base other than cytosine, in the nucleotide sequence of biological DNA.