The present disclosure relates to a novel antibody-drug conjugate (ADC) targeting claudin 18 isoform 2 (CLDN18.2), an active metabolite of the ADC, a method of producing the ADC, use of the ADC for the treatment and/or prevention of diseases, and use of the ADC for producing a drug for the treatment and/or prevention of diseases, more specifically hyperproliferative and/or angiogenic diseases, for example, cancer, and more particularly, to an antibody-drug conjugate including a novel antibody or antigen-binding fragment thereof that binds to CLDN18.2, and a pharmaceutical composition including the same.