The rapid dissemination of antibiotic resistance is threatening human health worldwide. Activated sludge system is a critical treatment technology for removing contaminants from wastewater. With the development of microbiological research technologies, increasing number of researches focus on antibiotic resistance in activated sludge. However, knowledge about antibiotic resistance and horizontal gene transfer in activated sludge remains largely unknown. Here, we review and discuss the research progress and main knowledge gaps of antibiotic resistance in activated sludge: (1) major determinants of antibiotic resistance in activated sludge; (2) methods used for analysis antibiotic resistance; (3) dissemination and spread of antibiotic resistance genes in activated sludge; (4) environmental risks of antibiotic resistance in activated sludge; (5) concluding remarks and future perspectives. This review will contribute to illuminating the microbial ecology driving the dissemination of antibiotic resistance, intending to support the development and optimization of wastewater treatment technologies and provide basis for developing management strategies to improve antibiotic resistance mitigation.