Neoadjuvant chemotherapy (NAC) is one of the main therapies for patients with local advanced breast cancer. CT and MRI have been used in combination with pathological examination in order to evaluate the efficacy of NAC. We present a case that showed discrepancies between the pathological findings and those of imaging analysis after NAC. We administered NAC to a patient with stage IIIB locally-advanced breast cancer. NAC showed remarkable drug efficacy. Clinical tumor response evaluated by CT and MRI showed a residual tumor. However, the pathological tumor response following NAC was grade 2b according to criteria of the Japanese Breast Cancer Society. Inaccurate determination of a residual tumor by MRI (a residual tumor diagnosed by MRI but a pathological complete response diagnosed by pathological examination) can occur occasionally.