Background: The patients receiving hematopoietic stem cell transplantation (HSCT) are known to have a high incidence of breakthrough nausea and vomiting due to the conditioning regimen. The purpose of this study was to evaluate the adequacy of antiemetic therapy for breakthrough nausea and vomiting in patients receiving HSCT and to propose an effective treatment regimen. Methods: We retrospectively reviewed the electronic medical records of 109 adult patients. The collected data were used to identify (1) antiemetic and dosing regimens prescribed for controlling breakthrough nausea and vomiting, (2) the rate of patients who developed breakthrough nausea and vomiting, and (3) the percent of antiemetics prescribed on the day of symptom onset. Based on the National Comprehensive Cancer Network guideline, we assessed the suitability of antiemetics for breakthrough nausea and vomiting, and prescription timing. Results: All patients were prescribed pro re nata antiemetics. About 40.0%, 41.4%, and 18.6% of patients were using one, two, and three or more additional drugs for breakthrough nausea and vomiting, respectively. The most frequently administered drugs were intravenous metoclopramide (43.8%) and granisetron patch (36.2%). Breakthrough nausea and vomiting occurred in 87 patients (79.1%) and they developed symptoms 320 cases. About 220 cases (68.8%) were treated with additional antiemetics on the day of symptom onset and the rate of symptom resolution was only 10.3% (9 patients). Conclusion: The breakthrough nausea and vomiting in patients receiving HSCT occurred very frequently and was hard to control, thus requiring more rapid and aggressive treatments.