Significance Antibodies are important therapeutic agents and have been used for the treatment of many diseases, including infectious and inflammatory diseases, and cancer. The therapeutic efficacy of an antibody is usually determined not only by the selectivity and affinity toward the target but also by the Fc-glycan structure interacting with the Fc receptors on immune cells. This study describes the preparation of various antibodies with different Fc-glycan structures as homogeneous glycoforms for the investigation of their effector activities. During this study, it was discovered that the biantennary N-glycan structure with two terminal alpha-2,6-linked sialic acids is a common and optimal structure that is able to enhance the activities of antibodies against cancer, influenza, and inflammatory diseases.