OBJECTIVE To investigate the nosocomial infection and risk factors of extended spectrum beta-lactamases (ESBLs),and the concomitant infection with other bacteria and double infection in patients of malignant hematopathy.METHODS Forty six malignant hematopathy patients with nosocomial infection by ESBLs positive bacteria were studied retrospectively.RESULTS ESBLs positive bacteria of nosocomial infection in patients of malignant hematopathy were Escherichia coli and Klebsiella.67.4% Were pulmonary infection and 30.4% with septicemia.Major risk factors were the usage of the third generation cephalosporin,the usage of chemotherapy and adrenal cortical hormone,and agranulocytosis.41.3% Cases had infection with other bacteria and 13.0% cases had double infection at the same time.All cases were sensitive to carbopenems,35.7% cases were sensitive to amikacin.CONCLUSIONS The prognosis of patients with nosocomial infection by ESBLs positive bacteria is bad.It is important to select appropriate chemotherapy,measure granulocyte amount in time,control the use of third generation cephalosporin and intensify support therapy.