Objective To investigate the infection prevention effect of prophylactic use of antibiotics for cancer inpatients with leukocyte count ≤ 1 × 109/L.Then to provide the basis for rational use of antibiotics.Methods It was retrospectively surveyed that the infection situation and prophylactic usage of antibiotics in the 426 cancer inpatients with leukocyte count ≤ 1 × 109/L caused by radiotherapy and chemotherapy.Results In the 426 inpatients,the infection rates of patients with and without prophylactic use of antibiotics were 11.0％ and 20.9％ respectively.The difference was statistically significant (x2 =6.815,P =0.009).The leukocyte count median values of patients with and without infection were 0.73 × 109/L and 0.77 × 109/L respectively.The difference had no statistical significance(Z =-1.257,P =0.209).The main infection sites were lower respiratory tract,upper respiratory tract and gastrointestinal tract with infection rates of 48％,12％ and 11％,respectively.The top five pathogens were Klebsiella pneumonia,Enterobacter cloacae,Escherichia coli,Enterobacter aerogenes and Staphylococcus aureus.The most use of antibiotics were cephalosporin.Conclusion When the leukocyte counts of cancer inpatients are less than or equal to 1 × 109/L induced by chemotherapy and radiotherapy,reasonable prophylactic use of antibiotics can reduce hospital infection rates.