Since the IFLA FRBR conceptual model, the transition to a data structure centered on entity-relationships has been underway. Reflecting this international trend, the draft of the 5th edition of the Korean Cataloging Rules (KCR5) were presented in May 2024. This study focused on the ‘relationship’ which provides additional information to users by connecting one entity with other entities. To this end, (1) the types of relationships between entities defined in the conceptual model and RDA cataloging rule were examined, (2) the actual cases of LC and PCC to record relationships in MARC21 based on RDA were analyzed, and finally (3) practical methods and challenges to be solved for applying them to KORMARC format were suggested. This study mainly utilized RDA training materials and data input guidelines of LC/PCC, and referred to full-MARC bibliographic records and authority records of LC and PCC participating libraries. This study aims to broaden the understanding of the new bibliographic structure and to prepare for the transition to the next-generation bibliographic structure such as BIBFRAME in the future.