For patients receiving high-dose chemotherapy, a 5-hydroxytryptamine 3 receptor antagonist combined with dexamethasone is a standard antiemetic therapy. Despite this prophylactic anti-emetic treatment, many patients still suffer from uncontrollable emesis. In this study, we retrospectively evaluated the antiemetic effectiveness and safety of aprepitant (a neurokinin-1 receptor antagonist) in addition to 5-HT₃ antagonist in Japanese patients with hematologic malignancy receiving high-dose chemotherapy prior to autologous peripheral blood stem cell transplantation (auto-PBSCT). Twenty-six patients received aprepitant and granisetron (the aprepitant group), whereas, 22 patients received granisetron alone (the control group). All patients received 3 mg of granisetron intravenously 30 min before chemotherapy administration. Patients in the aprepitant group additionally received 125 mg of aprepitant 60–90 min before administration of the first moderately to highly emetogenic chemotherapy. On the next day or thereafter, 80 mg of aprepitant was administered in the morning until the last administration of moderately to highly emetogenic anticancer drugs. The percentage of patients who achieved complete response (CR), defined as no emesis with only grade 1–2 nausea, in the aprepitant group was significantly higher than that in the control group (42% vs. 5%, p =0.003). Logistic regression analysis showed that non-prophylactic use of aprepitant was significantly associated with non-CR. The frequencies of adverse drug events (ADEs) were not significantly different between two groups. In conclusion, the results of this study suggest that the addition of aprepitant to granisetron can improve the antiemetic effect without increasing ADEs in patients receiving high-dose chemotherapy prior to auto-PBSCT.