Objective To study the specific killing effect of recombinant expression vector containing human breast cancer DF3 promoter and diphtheria toxin A fragment on human breast cancer cells in vivo.Methods thirty-six BALB/C nude mice were divided into four groups at random,each group has nine animals.Human breast cancer cells of DF3 positive and negative(MCF-7 and MDA-MB-231)were inoculated into corresponding animals respectively.Recombinant expression vector PGL3-DF3-DTA and PGL3-DF3 were inoculated into corresponding tumor when the animals grew up tumor.The tumor weight were measured and calculated continually.We killed the animals in different time and observed the morphological changes by means of light microscope.The apoptosis index of cells was evaluated by in-situ TUNEL.Immunocytochemical methods were used to detect the condition of lymphanglogenesis and angiogenesis in tumor.Results Human breast cancer xenograft model was established in nude mice successfully.The human breast cancer cells treated by PGL3-DF3-DTA showed a typical apoptosis morphology and TUNEL detection analysis revealed the apoptosis index of the treatment groups was significantly enhanced,which was associated with time and dosage.The expression of LYVE-1 and F8 were down regulated.Conclusion Recombinant expression vector PGL3-DF3-DTA could produce specific killing effect on human breast cancer cell line of DF3 positive in vivo.