The present invention relates to a pharmaceutical composition for preventing or treating hepatitis B, and a method for screening a hepatitis B treatment agent according to whether an HBV and a guanine-quadruplex (G-quadruplex) of a candidate material are formed, the pharmaceutical composition comprising, as an active ingredient, one or more oligonucleotides selected from the group consisting of: an oligonucleotide expressed by a nucleic acid sequence of SEQ ID NO: 1, 2, or 6, or a complementary nucleic acid sequence thereof； and an oligonucleotide having at least one chemical modification on said oligonucleotide. The pharmaceutical composition forms an HBV and a guanine-quadruplex and reduces covalently closed circular DNA (cccDNA) of the HBV, and thus can be used to treat or prevent hepatitis B.
