Seven genes (fabD, fabG, fabH, fabA, fabZ, fabB and fabI) of E.coli fatty acid biosynthetic enzymes were cloned by PCR amplifying and appropriate expression vectors were constructed. Under induction assay expression of plasmid encoded proteins was carried out in strain BL21(DE3) and seven enzymes were purified using Ni-NTA agarose resin. In the absence of [2-¹⁴C] malonyl-CoA fatty acid synthetic reaction was reconstituted in vitro by adding seven enzymes and co-factors. And several model reactions were established for identification of special fatty acid biosynthetic enzymes. Meanwhile Clostridium acetobutylicium FabZ function was characterized by this method.