Abstract: Objective: To investigate the value of 18F-fluorodeoxyglucose (FDG) PET-CT imaging in detecting axillary lymph node status of breast cancer, in comparison with CT imaging. Methods:A total of22patients treated with routine modified radical mastectomy who underwent 18F-FDG PET-CT imaging preoperatively were recruited in this retrospective study. PET-CT and CT images were reviewed. In CT imaging, the axillary lymph nodes were considered positive when the shortest diameter was longer than0.5cm (criterion A) or longer than or equal to 1.0 cm (criterion B) or the longest diameter was longer than or equal to1.0 cm (criterion C), respectively. In PET-CT imaging, the axillary lymph nodes were considered positive when abnormal 18 F-FDG uptake (criterion D) was seen or the maximum standardized uptake value (SUV max ) was larger than or equal to 1.0 for semiquantitative analysis (criterion E). All of the results were compared with histopathological results, and the diagnostic parameters of different diagnostic criteria were compared with each other. Results: There were statistical significances in the size and SUVmax in different diagnostic criteria between positive and negative axillary lymph nodes. PET-CT had the highest diagnostic accuracy and kappa value. Criterion A had the highest sensitivity (59.3%) and the lowest specificity (83.5% ). Criterion B had the highest specificity (98.2% ) and positive predictive value (PPV,72.7% ) and the lowest sensitivity ( 27.1%) and negative predictive value (NPV,8.4%). For criterion C, none of the diagnostic param-eters was of great value. For PET-CT, the results of visual assessment (criterion D) and semiquantitative analysis (criterion E) were identical and the accuracy ( 90.1%) and NPV (92.5%) were superior to those of CT; and the consistency with histo-pathological results was satisfacory (kappa value 0.57). The sensitivity (55.9% ), specificity (96.1% ) and PPV (71.7% ) of PET-CT were higher than those of CT in detecting positive axillary lymph nodes. The SUVmax of metastatic lymph nodes was higher than that of lymph nodes with no metastasis, with a significant difference ( P=0.000 ). Conclusion: 18F-FDG PET-CT was an effective and intuitive method for detecting axillary lymph node status of breast cancer patients.