Abstract:【Abstract】 Objective To explore the biological characteristics of phage DNAⅢ and its antidrugresistant tuberculosis potentials. Methods We observed morphological property of the plaques by doublelayer plating and ltrastructure of DNAⅢ by electron microscopy. We examined DNAⅢ's optimal muitiplicity of infection and its single step growth curve and inspected how DNAⅢ's survived was affected by temperature,pH value. We determined the host range of phage by Spot Test and the reaction constants between DNAⅢ antiserum and 33D, D29, Legendre, Leo, DNAⅢ, TM4, Bo4, Sedeg and Clark by neutralization test. Results The plaques of DNAⅢ were transparent and their sizes were about 1 mm in diameter. DNAⅢ had a long tail (208±287 nm in length). 104 MOI infected host bacteria gave the highest phage off springs. 0ur single step growth test showed that phage DNAⅢ had a latent period of 165 minutes and a burst size of 28 and it was sensitive to temperature and pH value. The susceptibility to phage DNAⅢ was also investigated with other clinical strains of drugresistant Mycobacterium tuberculosis. K value between antiserum and DNAⅢ is 77001 and there was little correlation among them. Conclusion Phage DNAⅢ is a suitable broad host range and low antigenicity siphoviridae phage which could be used in phage cocktail therapy.