Abstract: The present invention relates to a high-molecular weight oligonucleotides polymerization method which increases in vivo stability, and to the use of a high-molecular weight oligonucleotides prepared by the polymerization method. The oligonucleotide polymerization method of the present invention is advantageous in that an oligonucleotide with a small molecular weight can be easily polymerized into high-molecular weight oligonucleotides. Further, the high-molecular oligonucleotide prepared by the method of the present invention can bind to hydrophilic high-molecular materials or inorganic materials, and then can be stably delivered to a living body. Therefore, the high-molecular oligonucleotide prepared by the method of the present invention can be widely used for treating various diseases.