This study aimed to identify the risk factors of febrile neutropenia(FN)onset associated with melphalan(L-PAM)therapy. Thirty-nine patients(21 men, 18 women)were administered L-PAM intravenously for multiple myeloma(MM)from April 2011 to February 2022 at the Department of Hematology of Gifu Municipal Hospital. Patients were classified into those with and without FN(Grade 3 or higher), complete blood count and liver function tests were performed immediately before starting therapy. Univariate analysis with Fisher's exact probability test was performed. Factors with p<0.2 were considered as independent variables for multivariate analysis in the multiple logistic regression analysis. A multivariate analysis with 2 independent variables, lactate dehydrogenase(LD)level>222 U/L(upper limit of the facility reference value)and white <3.3×103/μL(lower limit of the facility reference value)from the univariate analysis, and FN onset(Grade 3 or higher)as the dependent variable showed that LD level>222 U/L(odds ratio: 6.33, 95% confidence interval: 1.12-35.8, p=0.037)was a significant factor. In conclusion, patients with LD levels >222 U/L immediately before starting therapy require adequate monitoring for FN onset following L-PAM administration.