Mirtazapine, which exerts an antagonistic effect on 5-hydroxytryptamine type 5-HT2A, 5-HT2C, 5-HT3 and H1 receptors, is considered useful for the prophylaxis of chemotherapy-induced nausea and vomiting (CINV). This study investigated the efficacy and safety of mirtazapine for the prevention of CINV in patients with thoracic cancer receiving platinum-based chemotherapy. A retrospective cohort study was conducted in patients with thoracic cancer receiving platinum-based chemotherapy with 15 mg mirtazapine once daily as a prophylactic antiemetic drug between January 2014 and December 2021. The effects of mirtazapine added to the standard antiemetic regimen for the prevention of CINV were evaluated in patients who had poor control of CINV in a preceding cycle and in patients who received the standard antiemetic therapy plus mirtazapine from their first cycle. A total of 35 patients were evaluated. Of these, 14 had poor control of CINV in a preceding cycle and received the standard antiemetic therapy plus mirtazapine in the next cycle. The rate of complete response in the delayed period in these patients was significantly improved from the preceding cycle to the next cycle (35.7% vs. 85.7%, p=0.018). In contrast, the other 21 patients had received the standard antiemetic regimen plus mirtazapine from the first cycle. The rate of complete response in the delayed period in these patients receiving the triplet antiemetic regimen plus mirtazapine as part of a cisplatin-based or carboplatin-based regimen and in patients receiving a doublet antiemetic regimen plus mirtazapine in a carboplatin-based regimen was 100%, 85.7% and 100%, respectively. No severe adverse events, including somnolence, were observed with the addition of mirtazapine. The addition of mirtazapine to the standard antiemetic regimen for CINV may be beneficial with acceptable safety when administered in association with platinum-based regimens to patients with thoracic cancer.