A 57-year-old female patient from Lucheng District was admitted to Wenzhou Central Hospital on September 28, 2021. The examination on admission showed the chronic disease face and clear consciousness; the skin and mucous membranes had no yellowish staining nor oedema but were scared. The patient was admitted to the cardiology department with “chest tightness pending further investigation” and was later transferred to the chemotherapy department due to cancerous pleural fluid. The patient had a recurrent fever since October 8. Laboratory tests showed the haemoglobin was 86 g/L, the red blood cell count was 2.74 × 10¹²/L suggesting moderate anaemia. The leukocyte count was 12.7 × 10⁹/L, the absolute neutrophil count was 10.6 × 10⁹/L. The patient also had mildly elevated total and indirect bilirubin; urine culture detects mixed growth of more than 3 bacteria, persistent urinary occult blood 2 +. Wright’s stain of the blood smear was performed on October 25, microscopic examination showed that 1-4 ringlets with purplish-red nuclei and blue cytoplasmic could be found in some red blood cells, which was considered to be a parasitic infection. The patient was a long-term resident of urban Wenzhou with no history of domestic or international travel, and no clear history of tick bites. The patient underwent breast-conserving surgery for left breast cancer in 2005, received chemotherapy and targeted drug therapy for multiple lung metastases between 2014 and 2021 and had 12 blood transfusions from June to October 2021. The PCR product of blood DNA amplificated by primers specific to Babesia was sequenced and identified with 99.43% homology to B. microti (GenBank accession: MG674832.1). The diagnosis of Babesia microti infection was confirmed. The patient was treated with oral chloroquine phosphate tablets (0.5 g/d, double the first dose for 5 d) and intravenous clindamycin (600 mg/d + saline 500 ml intravenously for 10 d), with some relief of symptoms, and parasites were still detected on microscopic examination after 5 days. The symptoms of high fever, jaundice and haemolysis caused by Babesia infection somewhat exacerbate the progression of terminal-stage cancer. On November 8, the patient died of multi-organ failure and unsuccessful resuscitation.