Objective To investigate the source of infection and the pathogenesis of listeriosis monocytosis in a case of maternal listeriosis， and to provide evidence for the prevention and control of listeriosis.Methods Field epidemiological investigation was carried out to collect case information， blood samples of patients， food samples in refrigerators and kitchen environment of families， food samples from farm product markets near families were collected， and Listeria monocytogenes in samples from different sources were detected.Results Patient often ate Chinese cold dishes purchased from farm product markets （5~7 times a week）， and made Chinese cold dishes at home or cut again. The food stored in the refrigerator of his family was not cooked， and the raw fruit roted in the refrigerator. Of the kitchen two chopping board unripe did not divide， clean disinfect not in time， kitchen operating surface existed cross pollution. The results showed that a total of 3 strains of Listeria monocytogenes were isolated from the 11 samples， one from the patient’s blood sample and two from food smear and cutting board smear in the kitchen refrigerator. It was suggested that this case was caused by the consumption of contaminated food and infected the fetus through the placental barrier.Conclusion This case was the first successful attempt to trace the source of listeriosis monocytosis infection in food and environment in Fengtai District. Listeria monocytogenes were detected in the raw meat， carrots， and kitchen samples in the refrigerator of the patient’s family. It was clear that the cross-contamination of food and environment caused the infection of listeria monocytogenes in the patient. Early recognition and treatment in hospitalis was an important guarantee to avoid adverse outcomes in neonates.