Asparaginase (ASNase) is one of the most important key drugs in the treatment of acute lymphoblastic leukemia (ALL). However, clinical hypersensitivity reactions often occur and lead to the discontinuation of ASNase treatment. Here, we report a retrospective study of 68 Erwinia ASNase (Erw-ASNase) administrations in 11 patients with childhood ALL who developed allergic reactions to E.coli-ASNase in our hospital between 2006 and 2012. The median age of the patients was 6 (range, 0 to 14). Erw-ASNase purchased overseas by the patients' guardians had already been administered when we obtained informed consent from the guardians. In all patients, fibrinogen and/or anti-thrombin III levels were decreased, but thrombosis did not develop. There was only one mild adverse event (grade 2 urticaria) in one patient, in whom Erw-ASNase could be continued after increasing the doses of premedication with antihistamine and prednisolone. Erw-ASNase could be safely administered to all patients.