Objective To trace the cause of a Listeria monocytogenes (LM) infected patient with acute lymphoblastic leukemia in Beijing, and to study the serotype,antimicrobial resistances and molecular characteristics of the associated strains. Methods The two strains isolated from peripheral blood of the patient at different times and the strain isolated from environmentally smeared sample were characterized by serotyping with polymerase chain reaction (PCR), antimicrobial susceptibility testing, pulsed field gel electrophoresis (PFGE) and multilocus sequence typing (MLST).Results Three isolates belonged to 1/2a-3a serotype,also had the same antimicrobial susceptibility result. All the strains were sensitive to penicillin, ampicillin, sulfamethoxazole, meropenem and erythromycin. They had the same PFGE pattern and MLST type ST155. Conclusion The living environment of patient was contaminated by LM. It was highly suspected that the strains isolated from lymphoblastic leckemia patient and the environmental smear sample had the same source.