The present invention relates to an antibody specifically binding to apoptosis inhibitor 5 (API5) protein and uses thereof. The antibody or antigen-binding fragment thereof that specifically binds to APIS according to the present invention can have excellent anticancer effects, such as inhibiting phosphorylation of ERK in cancer cells and inhibiting cancer growth. In addition, the antibody or antigen-binding fragment thereof exhibits excellent anticancer effects against cancers that are resistant or refractory to anticancer drugs. Accordingly, it is useful for preventing or treating cancers resistant or refractory to anticancer drugs as well as general cancers.