Abstract: cDNA including the 5′-terminal sequence of full-length mRNA with a cap structure is synthesized from a mRNA sample containing the full-length mRNA with the cap structure and non-full-length mRNA without any cap structure in mixture. At the first step, the phosphate group at 5′-terminus of the non-full-length mRNA in the mRNA sample is removed. At the second step, the cap structure at the 5′-terminus of the full-length mRNA in the mRNA sample is removed. At the third step, an oligoribonucleotide is ligated to the phosphate group at 5′-terminus of mRNA generated through the first and second steps. At the fourth step, mRNA with the oligoribonucleotide ligated at the 5′-terminus thereof at the third step is subjected to a reverse transcriptase process using a short-chain oligonucleotide capable of being annealed to an intermediate sequence within the mRNA as primer, to synthesize a first-strand cDNA.