Objective To evaluate the value of quantitative fluorescent PCR for detection of Mycobacterium tuberculosis(MTB)DNA in plasma(or serum).Methods The content of MTB DNA in the following samples was detected by real-time PCR,including 43 sera and 25 plasmas from tuberculosis patients,18 sera from the patients with non-tuberculosis pulmonary disease and 18 sera and 11 plasmas from healthy volunteers.Results MTB DNA was negative in 18 sera from the patients with non-tuberculosis pulmonary disease and all the specimens(serum and plasma)from healthy volunteers.The positive rate of MTB DNA in 55 tuberculosis patients was 18.2%(10/55).The positive rate was 27.8% in smear-negative TB patients compared with 13.5% in smear-positive TB patient group.The specificity of the detection of MTB DNA was 100%.Conclusions This study confirmed the existence of circulating MTB DNA in plasma and serum of tuberculosis patients and showed that the detection of MTB DNA may provide valuable information for the diagnosis of smear-negative TB patients.