Abstract: Objective This study aimed to assess the value of 18F-FDG PET in predicting pathological complete response （pCR） of breast cancer patients who underwent neoajuvant chemotherapy （NAC）. Methods Breast cancer patients diagnosed by core needle biopsy, who underHwent NAC subsequently, with 18F-FDG PET scanning both before starting after the completing of NAC, were retrospectively enrolled. Definitive surgery was performed for all patients with pCR status evaluated. Relative changes in maximum standardized uptake value （ΔSUVmax%） of breast tumor and axillary lymph node （ALN, if any） were calculated. Receiver operating characteristic （ROC） curves were used to assess the pCR predicting ability of ΔSUVmax%. Results In total, 87 patients were enrolled with the mean age of 46 years. pCR was noted in 30 （34.5%） patients by postoperative pathological examination. Thirty-six （41.4%）patients were categorized as CR by PET scanning before definitive surgery. The area under the ROC curve （AUC） of ΔSUVmax% was 0.802 （95%CI 0.680~0.893, P<0.000 1）, with the sensitivity of 61.90%, specificity of 87.50%. For the Luminal B（HER2-） subtype, the AUC was 0.907（95%CI 0.750~1.000,P=0.037）. We further found that, in the 41 patients diagnosed to have positive axillary lymph node （ALN） metastasis by pre-therapy PET/CT scanning, ΔSUVmax% also did very well in predicting the clearance of ALN metastasis, which AUC was 0.782（95%CI 0.625~0.895,P=0.000 1） with the sensitivity of 83.33%（95%CI 51.6%~97.9%） and the specificity of 68.97%（95%CI 49.2%~84.7%）. However, the predicting value of SUV changes was insignificant in other subtypes and in those with initially negative ALN. Conclusions Relative SUV change between pre-NAC and post-NAC 18F-FDG PET scanning is able to predict pCR in Luminal B （HER2-） subtype breast cancer, as well as clearance of ALN metastasis in patients with initially positive ALN.