Objective: To express recombinant human vascular endothelial growth factor (VEGF)121KDR/rGEL fusion toxin, specific to VEGF receptor 2 (VEGFR2) KDR, in E. coli, purify the expressed product and determine its biol. activity.Methods: The gene sequence of VEGF121KDR/rGEL fusion toxin were cloned into prokaryotic expression vector pET-32a(+), and the constructed recombinant plasmid pET-32a(+)-VEGF121KDR/rGEL was transformed to E. coli Origami (DE3) for expression under induction of IPTG.The expressed protein was purified by SP-Sepharose FF and NiSepharose FF chromatog., then digested with thrombin, further purified by Q-Sepharose FF chromatog., and determined for cytotoxicity to PAE/FLT1 and PAE/KDR cells on which VEGFR1/FLT1 and VEGFR2/KDR were highly expressed.Results: Restriction anal. and sequencing proved that recombinant plasmid pET-32a(+)-VEGF121KDR/rGEL was constructed correctly.The fusion protein of thioredoxin (Trx) as a tag and rhVEGF121KDR/rGEL, with a relative mol. mass of about 62 000, was expressed in a soluble form, and contained about 20% of total somatic protein.However, the relative mol. mass of purified rhVEGF121KDR/rGEL fusion toxin, after removal of tag, was about43 000, while the purity was more than 98%.The median inhibitory concentrations (IC50) of VEGFR1-pos. PAE/FLT cells was 278 nmol/L, which was more than 800 times of that of VEGFR2-pos. PAE/KDR cells (0.32 nmol/L).Conclusion: The rhVEGF121KDR/rGEL fusion toxin was successfully expressed in E. coli, which showed strong killing effect on vascular endothelial cells overexpressing VEGFR2.It laid a foundation of further study on the anti-tumor effect of the fusion toxin and development of novel drugs targeting tumors.