A 48-year-old woman with Parkinson disease (PD) suffered from auditory hallucinations (AH). We had treated her with a reduction in antiparkinsonian agents and the use of atypical antipsychotic agents. However, her symptoms did not improve, and her extrapyramidal symptoms (EPS) worsened. To lessen her depressive symptoms, treatment with a new-generation antidepressant, mirtazapine (MRZ), was commenced. The patient's AH gradually decreased with no worsening of EPS, and the AH disappeared 4 weeks after the commencement of treatment with MRZ. The present case suggests the effectiveness of MRZ for the treatment of refractory AHs in patients with PD.