Artemisinin-based combination therapy (ACT) has been the standard treatment for uncomplicated malaria. Although not licensed in Japan, artemether/lumefantrine (AL), one type of ACT, has been administered to patients with malaria since 2002 by the Research Group on Chemotherapy of Tropical Diseases. Herein, we reviewed malaria cases treated with AL in Japanese travelers. A retrospective study was conducted at the National Center for Global Health and Medicine from October 2005 to March 2013. There were 19 malaria patients treated with AL, and 10 falciparum malaria patients treated with AL only. In these 10 patients treated with AL only, the median time of fever clearance was 25.0 hours (range:14-66 hours), and the median time of parasite clearance was 36.0 hours (range:16-62 hours). There was a positive correlation between parasitemia and time from the start of therapy to the disappearance of the parasites. Parasitemia was higher (4.05% vs. 0.24%; p = 0.044) and parasite clearance time was longer (55.5 hours vs. 31.5 hours; p = 0.044) in the cases of recrudescence than non-recrudescence, respectively. Three of the 19 malaria patients showed recrudescence of malaria after treatment with AL. The reason that treatment failure was more frequently observed in this study than in previous reports may be related to poor absorption of lumefantrine owing to gastrointestinal symptoms, insufficiently ingested fatty foods, or high parasitemia on admission. The World Health Organization recommends that intravenous antimalarials should be administered in cases of severe malaria however, this is not applicable in Japan. Further studies are needed to distinguish patients with malaria who are treatable with ACT from those who should be treated initially with other intravenous antimalarials.