Four human vascular endothelial growth factor receptor Flt-1 cDNA fragments containing extracellular domain loops 2,1-2,2-3 and 1-3 respectively were amplified from human placental cDNA library by PCR and used for screening ligand binding domains by yeast two-hybrid system.The result showed that,not only loop 1-3,but also the smaller fragment loop 2-3 could bind bo hVEGF165.Recombinant expression plasmids pPIC9K/Flt-1(1-3)and pPIC9K/Flt-1(2-3)were constructed and transformed to Pichia.pastoris host strain GS115,cultured in flasks,and expressed under the induction of 1% methanol.The expressed product existed in supernatant in the form of soluble molecules and contained more than 60% of total protein after being induced for 4d.After being purified by CM-Sepharose FF and Sephacryl S-100 chromatography,its purity reached above 90%.Biological assay in vitro showed that the binding capacity of expressed soluble Flt-1(2-3)to hVEGF165 and its nhibiting effect on the proliferation of human umbilical reins endothelial cells(HUVEC)stimulated with hVEGF165 were close to those of s Flt-1(1-3).Animal test showed that sFlt-1(2-3)could nhibit the formation of regenerate blood vessels stimulated with hVEGF165 significantly.