Abstract: In order to investigate the effect of 6×His-tag on the solubility expression of linoleic acid isomerase (PAI) from Propionibacterium acne in E.coli, recombinant E.coli strains over-expressing PAI, PAIH (PAI fused with C-terminal his-tag) , HPAI (PAI fused with N-terminal his-tag) were constructed, respectively.Recombinant enzymes were analyzed by SDS-PAGE and Western blot.Enzyme activities were verified by gas chromatogram.Under similar growth and inducible expression conditions, three recombinant E.coli strains successfully expressed recombinant proteins which had linoleic acid isomerase activity.The total recombinant protein production levels of three recombinant strains were similar, His-tag had a noticeable negative effect on protein solubility and C-terminal His-tag had a bigger negative effect on solubility of the recombinant protein than N-terminal His-tag.