AIM To increase the production of recombinant des (1 - 3) IGF- I by increasing the copy number of genecarried on an expression vector, and to partially purify the expressed des (1 - 3) IGF-Ⅰ , as well as compareits bio-activity with standard IGF-Ⅰ.METHODS Second copy of des (1 - 3) IGF-Ⅰ gene was inserted into pExSecl/IGF-Ⅰ expression vectorconstructed by our previous work and carryed already one des (1 -3) IGF-Ⅰ gene, to form PExSec1/2 (IGF-Ⅰ) expression plasmid, which carried two copies of tandem des (1 - 3) IGF-Ⅰ gene. This plasmid wastranformed into a protease-deficient E. coli strain BL21 (DE3). The engineered bacteria was cultured andinduced at low temperature. The expressed product was purified through ultra-filtration and gel-filtration.The bio-activity of partially purified protein was tested by MTT method and compared with standard IGF-Ⅰ.RESULTS The amount of des (1-3) IGF-Ⅰ expressed by pExSec 1/2 (IGF-Ⅰ) reached up to 19% -22%of the total soluble bacterial protein, which is about 7% higher than that of des (1 -3) IGF-Ⅰ expressed bypExSec1/IGF-Ⅰ. The purity of recombinant des (1 - 3) IGF-Ⅰ reached 49% and 82% respectively after thetreatments by ultra-filtration and gel-filtration. The result of MTT assay showed that the bio-activity of des(1- 3) 1GF-I after gel-filtration was about 77% of that of standard IGF-Ⅰ at the same concentration.CONCLUSION The yield of recombinant des (1 - 3) IGF-Ⅰ was increased about 7% by construction ofexpression plasmid with two copies of des (1 -3) IGF-Ⅰ gene, compared with only one copy of gene,preliminarily purified des (1 -3) IGF-Ⅰ showed relatively high biological activity, which was about 77% ofthat of standard IGF-Ⅰ.