The drug-to-antibody ratio (DAR) value and dual-drug combination greatly influence the therapeutic index of antibody-drug conjugates (ADCs). The reported approaches usually require multifunctional branched linkers, a combination of complicated technologies, or protein-protein ligation, which may incorporate multihydrophobic fragments or result in low coupling efficiency. Herein, we developed a facile and efficient one-pot method to assemble dual-site-specific ADCs with defined DARs at both the N-glycosylation site and K248 site, either with the same payloads or with two types of payloads. The constructed dual-site ADCs showed acceptable homogeneity, excellent buffer stability, and enhanced in vitro and in vivo efficiency.